Influence of Knitted Fabric Construction

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Original article

Influence of knitted fabric constructionon the ultraviolet protection factor of greige and bleached cotton fabrics

Wai-yin Wong1, Jimmy Kwok-Cheong Lam1, Chi-wai Kan1 and

Ron Postle2

Abstract

The alarming increase of incidence of skin cancer has hastened development of ultraviolet (UV) protective clothing andresearch on UV protection of apparel. Although various fabric parameters that affect ultraviolet radiation (UVR) trans-mission were studied by researches, most of them focused on woven fabrics and chemical approach in enhancing UV

protection. There were few studies concerning knitted fabrics, in particular the influence of fabric constructions onultraviolet protection factor (UPF) and structural properties. The magnitude of transmission and scattering of UVRthrough a fabric is decided by fabric construction or knit structure, which is classified by geometrical arrangement of yarns and fibers of the fabric. This paper aimed at studying the influence of different knit structures upon the UPF withthe three main knit stitches incorporated in the knitted fabric constructions, namely the knit, tuck and miss stitches. TheUPF and structural characteristics, including thickness, weight, stitch density and porosity of greige and bleached knittedfabrics with different knit structures, are compared by adopting factorial analysis of variance. The results show thatfabrics with miss stitches possess a higher UPF than fabrics with tuck stitches. The double-knitted fabrics have better UVprotection than the single-knitted fabrics overall, but bleaching has different impacts on the UPF of single- and double-knitted fabrics. The study reveals that fabric thickness or weight cannot be used solely in explaining the UV protectiveperformance of knitted fabrics. However, fabric porosity can be a good indicator for UV protection when comparingfabrics with similar fabric weight and thickness but different structures or fiber contents.

Keywords

Ultraviolet protection factor, knit structures, weight, thickness, stitch density, porosity

Evidences were found globally that there is an increas-

ing number of people dying from skin cancer each year

and it is apparent that over-exposure to ultraviolet radi-

ation (UVR) is deemed to be one of the main reasons.1

Skin cancers are very common in the UK, with more

than 70,000 new cases diagnosed each year.2 In the US,

skin cancer is the most common cancer, which accounts

for nearly half of all cancer types with more than

2 million cases found each year.3 Skin cancer is also

the most common cancer type in Canada, which

accounts for an estimated one-third of all new cases

of cancer and its incidence rate continues to rise.4

Australia has the highest incidences of skin cancer in

the world which is almost four times the rates in the

UK, the US and Canada. Skin cancers account for 80%

of all newly diagnosed cancers in Australia and two in

three Australians will be diagnosed with skin cancer by

the time when they are 70.5 In Hong Kong, non-mela-

noma skin cancer is the eighth most common type of

cancer diagnosed, with over 717 new cases each year.6

The deleterious impacts caused by over-exposure to

UVR have increased the public awareness of the need

to adopt personal UV protective strategies, such as the

1Institute of Textiles and Clothing, The Hong Kong Polytechnic

University, Hong Kong2School of Chemistry, University of New South Wales, Australia

Corresponding author:

Jimmy Kwok-Cheong Lam, Institute of Textiles and Clothing, The

Hong Kong Polytechnic University, Hung Hom, Kowloon, Hong Kong.

Email: [email protected]

Textile Research Journal

83(7) 683–699

! The Author(s) 2013

Reprints and permissions:

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DOI: 10.1177/0040517512467078

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use of sunscreens on the parts of body that are exposed

to the sun. However, the protection provided by sun-

screens is not long lasting and requires frequent supple-

ment after a period of time due to continuous sweating

from the skin. Inappropriate usage of sunscreens, such

as applying an insufficient amount or thickness on the

skin, may attenuate the original UV protective ability.Although clothing, which acts as the ‘second skin’ of

human can provide some protection against harmful

UVR and the market value of UV protective clothing

is noteworthy, clothing can only provide limited protec-

tion against UVR, in particular for knitwear with a more

porous and stretchable structure than the woven gar-

ments. Many textile manufacturers try to enhance the

UV protective performance of garments using a chem-

ical approach with the use of dyes, whitening agents and

UV absorbers such as titanium dioxide or zinc oxide.

Nevertheless, the photodegradation of fabric dyes, opti-

cal brightening agents and the potential hazard of these

chemicals to the human body lacks investigation. The

study of Khazova et al.7 indicated that there is a degrad-

ation of efficiency of the optical brightening agents, as

well as photochemical degradation of fabric dyes after

prolonged exposure to UVR. It reveals the problems

about the sustainable function provided by UV protect-

ive finishing on textile products, including pollution and

excessive water consumption brought by chemical treat-

ments giving rise to environmental concerns. Many

researchers have studied various fabric parameters that

influence UVR transmission, such as fiber compos-

ition,8–11 fabric construction,11–16 yarn twist,17,18 thick-

ness,8,10,19

weight,19

wetness or moisture content,20–22

stretch or extensibility,20,22,23 chemical treatment or

additives and coloration.24–32

However, most of the studies have concentrated on

the above fabric parameters with woven fabrics only,

whereas there have been few studies concerning knitted

fabrics, in particular the influence of knitted fabric con-

struction on UV protection. Stankovic et al.17 and

Wilson and Parisi20 have studied UV protection prop-

erties with knitted fabrics, but neither of them expli-

cated how the knit structures exactly influence UV

protection of fabrics., Stankovic et al.17 studied the

ultraviolet protection factor (UPF) of grey-state plain

cotton knitted fabrics by investigating the impact of

yarn twist and surface geometry instead of the knitted

fabric constructions. Wilson and Parisi20 compared the

UV protection provided by two knit structures (eyelet

and pique) and two weave structures; however, the fab-

rics were composed of different fiber contents. The UV

protective ability of fabric depends on the amount of

UVR reflected or absorbed by fibrous materials, trans-

mitted through pores between fiber and yarn, and also

scattered within the fabric layer. Fabric construction is

one of the important factors affecting these paths for

UVR. The arrangement of yarns and fibers determined

by fabric construction can influence the compactness of

the structure, together with the open space within the

fabric. Other physical properties, such as the amount of

open area produced when tension is applied or the

amount of shrinkage after laundering, are presumably

in connection with fabric construction.Moreover, many researchers agree that dyes can

increase the UVR blocking property of a fabric and

darker colors can provide better UV protection. The

use of UV absorbers even gives excellent UV blocking

performance to fabric. Nonetheless, knitted fabrics have

more complex fabric geometry, rather a porous structure

and are more elastic than woven fabrics. It should be

noted that the UV protection of fabrics enhanced by

chemical treatment is only sufficient when the fabric

structure is compact enough.14 Knitted fabrics are

easily deformed or stretched during wearing due to

their elastic characteristics. The fabric layer will

become thinner when it is worn next to skin and more

open spaces will be created for transmitting UVR in the

actual end-use. Moon and Pailthorpe22 found that there

is 15.5% elongation on average when fabrics are in con-

tact with the body and this caused a remarkable reduc-

tion of UPF. The increase of the UVR penetration is

almost linear with stretch.14 It can be anticipated that

the UV protection provided by the chemical approach

may not always be effective because of the actual wear-

ing condition of garments. Although darker shaded

clothing can provide better UV protection than those

with pastel colors, more infrared (IR) radiation is

absorbed and heat is generated simultaneously, whichmakes the wearers feel unpleasant under hot conditions.

Therefore, a balance between UV protection and ther-

mophysiological comfort is essential when developing

UV protective garments.

This paper aimed at studying the UV protection

property of knitted fabrics from a fundamental level

by considering how the modification of knitted fabric

construction can improve the UV protective ability of

fabrics, instead of using a chemical approach as a sec-

ondary level. Fabric construction is deemed to present

the simplest and cheapest solution to achieve good UV

protection without additional finishing processes.31

From the literature review, fabric construction has

been proposed as one of the most important variables

affecting UVR transmission, especially when light pastel

colored fabrics were used as UV protective clothing.14

Experimental details

Materials

In this study, 10 fabric constructions were examined

wherein four structures are single-knitted fabrics and

684 Textile Research Journal 83(7)



the other six are double-knitted fabrics. Single-knitted

fabrics are knitted with one set of needles, whereas

double-knitted fabrics are knitted with two sets of nee-

dles, either rib or interlock gating. Different knitted

fabric constructions were designed based on the com-

bination of three basic knit stitches – knit, tuck and

miss stitches – which are shown in Figure 1. The yarn

path diagrams for the 10 constructions are illustrated

in Figure 2.

Fabric specimens were knitted using a Stoll CMS

822 14 G computer flat knitting machine using 100%

combed organic cotton yarn. Plied yarns were used

with the yarn count 3/40 s (three single yarns of

40 cotton counts were combined in the yarn feeding

to get a plied yarn). It is usual practice for knitwear

production to have plied yarns for knitting instead of

one single yarn with the same yarn count in order to

achieve higher strength, uniformity, better abrasion and

fabric appearance. The approximate yarn count for the

plied yarn is 42 tex and the calculated yarn diameter is

0.01 inch, according to the cloth geometry by Peirce33

and Booth.34

Apart from untreated greige fabrics, another set of

greige fabric specimens were scoured and bleached to

remove the natural pigments and impurities in order to

investigate the impact of bleaching against UV protec-

tion among various knitted fabric constructions. The

cotton knitted fabrics were scoured and bleached in a

Figure 2. Yarn path diagrams of different knitted fabric constructions.

Figure 1. Basic knit stitches viewed from the fabric face: (a) knit stitch; (b) tuck stitch; (c) miss stitch.

Wong et al. 685



combined process at laboratory conditions with 4 g/l

hydrogen peroxide, 6 g/l sodium hydroxide, 0.5 g/l sta-

bilizer and 0.5 g/l wetting agent. Hydrogen peroxide

was chosen as the bleaching agent to minimize the

damage on fabrics during the bleaching process.

Test methods

Assessment of ultraviolet protection factor

The UV protective ability of fabrics is commonly

expressed in terms of UPF. The UPF of fabric speci-

mens was measured using a Cary 300 Conc ultraviolet-

visible (UV-Vis) spectrophotometer equipped with an

integrating sphere and a Schott UG filter for minimiz-

ing any measurement error caused by fluorescence.

UPF measurement was conducted corresponding to

the Australian/New Zealand Standard AS/NZS

4399:1996.35 Fabric specimens were evaluated in a

dry, flat and tensionless state with measurements

taken in both machine and cross-machine directions

of the fabric. All fabric specimens were conditioned

under standard environment for 24 hours prior to

assessment.36 The transmittance over a wavelength

range of 290–400 nm with 5 nm intervals was measured

using the spectrophotometer for calculating the UPF of

fabric specimens using Equation (1):37,38

UPF ¼ E eff

E 0 ¼

P400nm290nm E S P400nm

290nm E S T ð1Þ

The UPF is defined as the ratio of the average effectiveUVR irradiance calculated for unprotected skin (E eff )

to the average effective UVR irradiance calculated for

the skin protected by test fabric (E 0), where E is the

relative erythemal spectral effectiveness, S is solar

spectral irradiance in Wm2 nm1, T is the spectral

transmittance of the fabric, is the wavelength in nm

and is the bandwidth in nm. Although definitions of

UVR and ultraviolet B (UVB) given in the standards

start at 280 nm, the measurement of UVR transmission

of the specimen records from 290 to 400 nm. The UVR

irradiance at wavelengths below 290 nm is not used in

the calculations because these wavelengths are unlikely

to reach the Earth’s surface.35 The inclusion of these

wavelengths in the calculations would preclude the use

of some otherwise acceptable spectrophotometers and

spectroradiometers.

Fabric thickness, weight and stitch density

Thicknesses of fabric specimens were measured corres-

ponding to the standard test method ASTM D1777-96

(Reapproved 2011).39 A calibrated digital thickness

tester with counter balance was used to measure the

thickness without distortion in a plane parallel to the

presser foot and anvil. Fabric weight was measured in

accordance with the standard test method ASTM

D3776-09 (Option C for small swatch fabric).40 The

stitch densities of fabric specimens were obtained by

counting the number of courses and wales to the near-

est half stitch. As there are rather complex fabric con-structions being assessed, such as rib, cardigan and

Milano, the wales and courses recognized on visual

inspection of the fabric may be made up of two or

more structures. The determination of the number of

stitches per unit area was acquired.

Porosity

Previous studies found that porosity is an important

indicator for UV protection performance of a

fabric.8,41–45 When UVR strikes the fabric, it can be

reflected, absorbed by fiber, scattered within the

fabric layer and transmitted through fibers and fabric

pores.18 The incident radiation passing through fabric

is largely dependent on the percentage of volume within

a fabric in which there is no fiber in that volume from

the fabric face to back.46 Therefore, the three-

dimensional nature of fabrics with various knit struc-

tures can be investigated by considering the fabric por-

osity instead of either fabric thickness or fabric weight

only. The more porous structure of the fabric will result

in a higher porosity, while a tighter structure gives a

lower porosity. Knitted fabrics usually have a higher

porosity than woven fabrics.47

Various methods of determining the porosity of porous materials were

firstly developed in the field of petroleum technology,

wherein the gravimetric method has been applied to

fabrics.44 Porosity can be defined as the proportion of

void space within the boundaries of a solid material,

compared to its total volume; in other words, it is the

fraction of void space in a porous medium.47–49

Porosity is usually expressed in percentage (%); the cal-

culation is shown in Equation (2):

PorosityðÞ ¼ 100 1 t

m ð2Þ

where t is the bulk density (g/cm3) and m is the fiber

density (g/cm3). The fiber density of cotton, 1.54 g/cm3,

was substituted in the equation for calculation.50 The

calculation of bulk density (g/cm3), t, of a knitted

fabric is obtained by Equation (3), where M is the

mass per unit area of fabric and V is the volume of

the unit area of fabric:51,52

t ¼M

V ð3Þ




The volume of the unit area of fabric is simply equiva-

lent to the geometrical fabric thickness, t, and therefore

calculation of bulk density can be summarized as

Equation (4):51

Bulk Density ðg=cm3Þ ¼ M ðg=cm2Þ

t cmð Þ ð4Þ

Visual assessment on fabric pores

Different fabric constructions give a unique fabric sur-

face appearance as well as the size of fabric pores,

which determines the amount UVR transmission.

The fabric pores of greige and bleached knitted fabrics

with different structures were assessed visually through

the microscope under standard condition. A stereo

microscope Lecia M156C was used to capture the

micrographs with 25.0 magnification. The micro-

graphs of greige and bleached single-knitted fabrics

and double-knitted fabrics are shown in Figures 3and 4, respectively.

Analysis

In order to systematically study the impact of knit

structures and bleaching on the UV protective

Figure 3. Micrographs of greige and bleached single-knitted cotton fabrics at gauge length 14 G: (a) all knit; (b) knit & tuck; (c) knit &

miss (25%); (d) knit & miss (50%).

Wong et al. 687



Figure 4. Micrographs of greige and bleached double-knitted cotton fabrics at gauge length 14 G: (a) 1 1 rib; (b) half cardigan;

(c) full cardigan; (d) half Milano; (e) full Milano; (f) interlock.




performance in relation to the structural parameters of

knitted fabrics, factorial analysis of variance

(ANOVA) was conducted. It identifies the existence

of significant differences in various variables studied,

which includes the UPF and fabric structural proper-

ties covering fabric weight, thickness, stitch density

and porosity among different knit structures. Any dif-ferences between the variables studied were considered

as significant if the p-value was less than or equal to

0.05. The interaction effect and main effect were iden-

tified among groups of variables. The effect size stat-

istics (partial eta squared) were examined to indicate

the proportion of variance of the dependent variable

that is explained by the independent variable.53

It reveals the relative magnitude of the differences

between means, or the amount of total variance in

the dependent variable that is predictable from know-

ledge of the levels of the independent variable.54 The

effect size can be classified as small (partial eta

squared ¼ 0.01), medium (partial eta squared ¼ 0.06)

and large (partial eta squared ¼ 0.14) according to

Cohen’s criterion.55 Post-hoc tests were performed

for a whole set comparison by exploring the differ-

ences between each of the fabric construction groups

in the study. Post-hoc tests compare each pair of

groups systematically and indicate whether there is a

significant difference in the means of dependent vari-

ables. Since single-knitted fabrics and double-knitted

fabrics have very distinct fabric constructions and

structural properties, their results are discussed and

analyzed separately to achieve a more accurate eluci-

dation. In addition, a paired-samples t-test was usedto compare the mean scores of the UPF and structural

parameters of the same groups of fabrics before and

after bleaching in order to determine the impact of

bleaching on the UPF and the structural parameters

studied.

Apart from analyzing the results by ANOVA, the

relationships between the UPF and the four struc-

tural parameters were explored by a correlation ana-

lysis. This determines the degree to which the

variables are related by using the Pearson correlation

coefficient (r). It is obtained from the correlation

analysis, which ranged from 1 to + 1, in other

words, from negative correlation to positive correl-

ation between two variables. The size of the absolute

value of r provides an indication of the strength of

the relationship. According to Cohen’s suggestions,

the strength of correlation can be divided into

three levels: small (r ¼ 0.10–0.29), medium (r ¼ 0.30–

0.49) and large (r ¼ 0.50–1.0).55 Preliminary analyses

were performed by generating a scatterplot for

each pair of variables to ensure no violation of

the assumptions of normality, linearity and

homoscedasticity.53

Results and discussion

The UPF and the main structural parameters – fabric

thickness, fabric weight, stitch density and porosity of

different knitted fabric structures – are shown in

Figures 5–9, respectively. The error bars in these figures

represent 95% confidence interval for variability of thedata collected.

Ultraviolet protection factor of single-knitted

cotton fabrics

The results of the ANOVA summarized in Table 1 indi-

cate that the UPF significantly differs among the four

single-knit structures (F 3,16 ¼ 79.824, p 0.05), greige

and bleached fabrics (F 1,16 ¼ 51.705, p 0.05) and

there is an interaction between knit structures

and bleaching (F 3,16 ¼ 23.346, p 0.05) affecting the

UPF. The effect sizes of knit structure (partial

eta squared ¼ 0.937), bleaching (partial eta

squared ¼ 0.764) and the interaction (partial eta

squared ¼ 0.814) are large. Although the existing inter-

action denotes that the structure of specimen was

affected by bleaching, the effect size of the knit struc-

ture is larger than bleaching, as well as larger than the

interaction effect. Most of the single-knitted fabric spe-

cimens exhibited a significant increase in UPF after

bleaching, except the all knit, as shown in Figure 5(a)

(t11 ¼ 2.73, p 0.05, two-tailed). Some studies

reported that bleaching caused an increase in UVR

transmission of cotton fabrics because of the removal

of natural pigments and lignin, which can absorb UVR;however, it should be noted that the fabrics studied

were mostly woven fabrics.8,42,43 Nevertheless, shrink-

age in the fabric caused by bleaching closed the small

gaps between yarns and resulted in less UVR

transmission.

The post-hoc test compares each pair of single-knit

structures and indicates whether there is a significant

difference in the means of the UPF. It shows that most

of the single-knit structures significantly differ from

each other ( p 0.05). The largest significant difference

in UPF for greige single-knitted fabrics exists between

the knit & miss (50%) (Mean ¼ 7.28, SD ¼ 0.37) and

knit & tuck (Mean ¼ 3.77, SD ¼ 0.29). The situation

changed after bleaching, with the largest difference in

UPF occurring between the knit & miss (50%)

(Mean ¼ 8.76, SD ¼ 0.54) and all knit (Mean ¼ 5.96,

SD ¼ 0.35). In general, single-knitted fabrics with knit

& miss structures offer a higher UPF than the all knit,

whereas the knit & tuck structure gives the lowest UPF

in the greige stage. The long straight float of miss stitch

reduces the elasticity of fabric by pulling the adjacent

columns of wale closer together and, thus, less open

spaces are present for transmitting UVR. The knit &

Wong et al. 689



miss (50%) has more miss stitches than the knit & miss

(25%) as well as higher UPF. The micrographs shown

in Figure 3(c) and (d) provide a comparison between

these two structures with a higher number of wales per

unit length in the knit & miss (50%) than that in the

knit & miss (25%) for both greige and bleached stages.

The knit & tuck incorporated with tuck stitches has a

lower UPF overall because the side limbs or legs of the

tuck loop are not restricted at the feet by the head of an

old loop and therefore the tuck loops tend to straighten

themselves, causing the loops in the adjacent wales to

be pushed apart. The presence of tuck loops made the

Figure 5. Ultraviolet protection factor (UPF) of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G

(with error bars): (a) UPF of single-knitted fabrics; (b) UPF of double-knitted fabrics.

Figure 6. Thickness of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G (with error bars):

(a) thickness of single-knitted fabrics; (b) thickness of double-knitted fabrics.




fabrics bulkier and wider. Fabrics with knit & tuck

structures have a lower number of wales per unit

length with larger fabric pores, as shown in

Figure 3(b), than the other single-knit structures.

Ultraviolet protection factor of double-knitted

cotton fabrics

Both greige and bleached double-knitted fabrics have a

generally higher UPF (ranging from UPF 6.5 to 38.8)

than the single-knitted fabrics (ranged from UFP 3.8 to

8.8). Double-knitted fabrics are produced with two

sets of needles, with the second needle bed located at

a right angle to the first bed of needles. Hence, there is

one more layer of fibrous materials to absorb the UVR,

as well as greater the probability that the incident UVR

will encounter more fibers along its path.18 A general

comparison of UPF values for various double-knitted

fabric structures is shown in Figure 5(b). There are

significant differences between the UPF of the six

Figure 7. Fabric weight of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G (with error bars):

(a) fabric weight of single-knitted fabrics; (b) fabric weight of double-knitted fabrics.

Figure 8. Fabric stitch density of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14 G (with error

bars): (a) stitch density of single-knitted fabrics; (b) stitch density of double-knitted fabrics.

Wong et al. 691



double-knit structures (F 5,24 ¼ 5.348, p 0.05), the UPF

of greige and bleached double-knitted fabrics

(F 1,24 ¼ 516.202, p 0.05), and an interaction exists

between knit structures and bleaching (F 5,24 ¼ 21.325,

p 0.05), which influenced the UPF as shown in

Table 1. Contrary to the results of the single-knitted

fabrics, bleaching (partial eta squared ¼ 0.956) has a

greater influence upon the variance in UPF of double-

knitted fabrics than the knit structures (partial eta

squared ¼ 0.527) and also the interaction (partial eta

squared ¼ 0.816). The UPF of the six double-knitted

fabrics decreased significantly after bleaching

Table 1. Summarized results of the two-way between-groups analysis of variance (ANOVA) for ultraviolet protection factor (UPF)

and structural parameters of fabric specimens

Single-knitted fabrics Double-knitted fabrics

Dependent variables

Independent

variables F test p-value

Partial eta

square F test p-value

Partial

eta square

UPF Structures F 3,16 ¼ 79.824 0.000 0.937 F 5,24 ¼ 5.348 0.002 0.527

Bleaching F 1,16 ¼ 51.705 0.000 0.764 F 1,24 ¼ 516.202 0.000 0.956

Interaction F 3,16 ¼ 23.346 0.000 0.814 F 5,24 ¼ 21.325 0.000 0.816

Fabric thickness Structures F 3,16 ¼ 173.333 0.000 0.970 F 5,24 ¼ 76.091 0.000 0.941

Bleaching F 1,16 ¼ 3640.474 0.000 0.996 F 1,24 ¼ 1464.266 0.000 0.984

Interaction F 3,16 ¼ 26.298 0.000 0.831 F 5,24 ¼ 32.596 0.000 0.872

Fabric weight Structures F 3,16 ¼ 128.228 0.000 0.960 F 5,24 ¼ 473.943 0.000 0.990

Bleaching F 1,16 ¼ 2701.279 0.000 0.994 F 1,24 ¼ 1225.925 0.000 0.981

Interaction F 3,16 ¼ 15.053 0.000 0.738 F 5,24 ¼ 269.254 0.000 0.982

Stitch density Structures F 3,16 ¼ 308.314 0.000 0.983 F 5,24 ¼ 448.017 0.000 0.989

Bleaching F 1,16 ¼ 425.658 0.000 0.964 F 1,24 ¼ 77.63 0.000 0.764

Interaction F 3,16 ¼ 9.747 0.001 0.646 F 5,24 ¼ 14.214 0.000 0.748

Calculated Porosity Structures F 3,16 ¼ 45.958 0.000 0.896 F 5,24 ¼ 91.179 0.000 0.950Bleaching F 1,16 ¼ 0.292 0.596 0.018 F 1,24 ¼ 87.908 0.000 0.786

Interaction F 3,16 ¼ 7.423 0.002 0.582 F 5,24 ¼ 24.843 0.000 0.838

Figure 9. Porosity of greige and bleached, single- and double-knitted cotton fabrics at gauge length 14G (with error bars):

(a) porosity of single-knitted fabrics; (b) porosity of double-knitted fabrics.




(t17 ¼ 8.61, p 0.05, two-tailed), which is opposite to

the results of the four single-knitted fabrics. The results

here agree with previous studies, which stated that

bleaching causes more UVR to be transmitted through

the bleached cotton fabrics because of the absence of

natural pigments and impurities. The impact of shrink-

age for the double-knitted fabrics resulted from bleach-ing does not overcome the effect of bleaching, which

happened in the single-knitted fabric specimens.

Double-knitted fabrics are more dimensionally stable

and compact than single-knitted fabrics. The double-

knitted fabrics are unlikely to be stretched or deformed

during the process of bleaching. This conforms to the

results shown in Table 1 that there is a smaller effect

size of the interaction between bleaching and structures

(partial eta squared ¼ 0.816) than the effect of bleaching

alone (partial eta squared ¼ 0.956). The results of UPF

for the bleached double-knitted fabric specimens can be

explained with a more evident inference than the greige

double-knitted fabric specimens containing the natural

pigments and impurities.

The results of the post-hoc test show that most of the

double-knitted structures significantly differ from each

other ( p 0.05). The largest difference in UPF is found

between the greige half Milano (Mean ¼ 38.84,

SD ¼ 2.75) and greige interlock (Mean ¼ 25.85,

SD ¼ 1.61). After bleaching, the largest difference in

UPF is found between the bleached full cardigan

(Mean ¼ 6.52, SD¼ 0.31) and bleached interlock

(Mean ¼ 23.35, SD ¼ 0.51). The bleached interlock

obtains the highest UPF, followed by the bleached

Milano and bleached 1 1 rib, while the bleached car-digan possesses the lowest UPF. The interlock fabrics

are produced with interlock gating in which the col-

umns of wales are directly behind each other on both

the fabric face and back. They have a dimensionally

stable structure that does not tend to be stretched

easily. A compact structure in the interlock fabrics

can be observed from Figure 4(f), showing that adja-

cent columns of wale are packed closely together giving

a firmer fabric structure with less amount and smaller

size of fabric pores. However, fabrics other than the

interlock structure that were produced with rib gating

obtain a relatively lower UPF. In rib gating, the needles

of one bed are located in the spaces between the needles

of the other bed and the fabrics are more extensible in

the course-wise direction. The full Milano and half

Milano obtain the second-highest UPF after bleaching

because of the miss stitches incorporated in the fabric

structures. The only difference between the full Milano

structure and half Milano structure is that one more

course is knitted on the front needle and missed at

the back. There are more miss stitches in the full

Milano fabric structure than the half Milano, which

results in higher UPF. The cardigan fabrics possess

a lower UPF in the bleached specimens than the

Milano fabrics because the tuck loops in cardigan fab-

rics extend the fabric in the course-wise direction and

larger fabric pores are created, which are illustrated in

Figure 4(b)–(e). As there are more tuck stitches in the

construction of the full cardigan than that of the half

cardigan, the UPF of the bleached full cardigan is lowerthan the bleached half cardigan.

Fabric thickness of single-knitted cotton fabrics

The results of the ANOVA in Table 1 show that there

are statistically significant differences in fabric thickness

among the four single-knit structures (F 3,16 ¼ 173.333,

p 0.05), greige and bleached fabrics (F 1,16 ¼ 3640.474,

p 0.05) and there is an interaction between knit struc-

tures and bleaching (F 3,16 ¼ 26.298, p 0.05) affecting

the fabric thickness. The effect sizes of knit structure

(partial eta squared ¼ 0.97), bleaching (partial eta

squared ¼ 0.996) and the interaction between knit

structures and bleaching (partial eta squared ¼ 0.831)

are large. There is a significant increment of fabric

thickness among the four single-knit structures after

bleaching, as shown in Figure 6(a) (t11 ¼ 21.29,

p 0.05, two-tailed). The results of the post-hoc test

also reveal there are the largest differences in fabric

thickness between the greige knit & miss (50%)

(Mean ¼ 0.95, SD ¼ 0) and greige knit & miss (25%)

(Mean ¼ 0.82, SD ¼ 0.02), and also between the

bleached knit & miss (50%) (Mean ¼ 1.48, SD ¼ 0.01)

and bleached all knit (Mean ¼ 1.19, SD ¼ 0.01). In both

greige and bleached stages of fabrics, knit & tuck hashigher thickness than knit & miss (25%), but the results

in UPF for these two structures are reversed. Although

the miss stitches in the fabric construction can make the

fabric narrower in width, while tuck stitches increase

the width of fabric as well as the fabric thickness, the

fabric pores within the knit & tuck fabrics are larger

than the other knit structures, as shown in Figure 3(b),

and more UVR can be passed through the fabric pores

directly. It contradicts the general concept that a

thicker fabric can give better UV protection regardless

of the fabric structure and porosity.

Fabric thickness of double-knitted cotton fabrics

Double-knitted fabrics have the significant differences

in fabric thickness among the six double-knit structures

(F 5,24 ¼ 76.091, p 0.05), greige and bleached fabrics

(F 1,24 ¼ 1464.266, p 0.05) and interaction exists

between structure and bleaching (F 5,24 ¼ 32.596,

p 0.05). Knit structure (partial eta squared ¼ 0.941),

bleaching (partial eta squared ¼ 0.984) and the inter-

action between knit structures and bleaching (partial

eta squared ¼ 0.872) have large effect sizes. The overall

Wong et al. 693



thickness of double-knitted fabric specimens shown in

Figure 6(b) indicated the thickness increased signifi-

cantly after bleaching (t17 ¼ 12.03, p 0.05, two-

tailed). From the results of the post-hoc test, the largest

differences in fabric thickness are found between the

greige half cardigan (Mean ¼ 1.53, SD ¼ 0.06) and

greige 1 1 rib (Mean ¼ 1.23, SD ¼ 0.02), and alsobetween the bleached interlock (Mean ¼ 1.98,

SD ¼ 0.01) and bleached 1 1 rib (Mean ¼ 1.53,

SD ¼ 0.02). In the greige stage, the half cardigan has

the highest thickness, while the 1 1 rib possesses the

lowest thickness. However, the situation changed after

bleaching in which the bleached interlock obtains the

highest thickness and the bleached 1 1 rib has the

lowest thickness again. The interlock has the greatest

change in fabric thickness by 46.7% after bleaching,

which results in the variation in UPF of interlock fab-

rics, with the lowest UPF among structures in the

greige stage becoming the structure that possesses

the highest UPF after bleaching. This agrees with the

results in the effect size of bleaching in double-knitted

fabrics (partial eta squared ¼ 0.956), which has a

greater influence upon the variance in UPF than the

knit structures of double-knitted fabrics (partial eta

squared ¼ 0.527).

The correlations between UPF and fabric thickness

of single- and double-knitted fabrics in greige and

bleached stages are studied and the results are indicated

in Table 2. Positive correlations are found between the

UPF and the fabric thickness of bleached single-knitted

fabrics (r ¼ 0.821, p 0.05) and the bleached double-

knitted fabrics (r ¼ 0.6, p 0.05), which both have alarge strength of correlation (r ¼ 0.50–1.0). The higher

the thickness of bleached fabrics, the better UV pro-

tective ability obtained. However, this is not always

true when comparing different knit structures, such as

the bleached knit & tuck, with the second-highest thick-

ness but also the second-lowest UPF among the single-

knit structures. There are no significant correlations

between UPF and thickness of the greige single-knitted

fabrics (r ¼ 0.298, p ¼ 0.347) and greige double-

knitted fabrics (r ¼ 0.416, p ¼ 0.086). The variation in

fabric thickness of the greige single- and double-knitted

fabrics may not significantly affect the UV protection

performance because of the natural pigments and

impurities that absorb a certain amount of UVRalready.

Fabric weight of single-knitted cotton fabrics

Similar to the results of fabric thickness, the results of

the ANOVA in Table 1 indicate that the fabric weight

of single-knitted fabrics differ significantly in structures


(F 1,16 ¼ 2701.279, p 0.05) and an interaction exists

between knit structures and bleaching (F 3,16 ¼ 15.053,

p 0.05) that has an impact on fabric weight. The effect

sizes of knit structure (partial eta squared ¼ 0.96),


action (partial eta squared ¼ 0.738) are also large.

There is an overall increment of fabric weight among

the single-knitted fabrics after bleaching, as shown in

Figure 7(a) (t11 ¼ 23.69, p 0.05, two-tailed). The

results of the post-hoc test show that the greige knit

& miss (50%) (Mean ¼ 184.49, SD ¼ 2.93) and greige

knit & tuck (Mean ¼ 153.58, SD ¼ 3.98) obtain the lar-

gest difference in fabric weight, and also between the

bleached knit & miss (50%) (Mean ¼ 280.25,

SD ¼ 3.87) and bleached all knit (Mean ¼ 224.03,

SD ¼ 4.43). Although the knit & tuck and knit & miss(25%) have similar fabric weights in both greige and

bleached stages, the UPF of the greige knit & tuck is

lower than that of the greige knit & miss (25%). Fabrics

with similar fabric weight do not have the resembling

UV protective performance because of the distinct

fabric structures and other factors, such as size of

fabric pores.

Table 2. Pearson correlation coefficients (r ) between the ultraviolet protection factor (UPF) and the structural

parameters of fabric specimens

Structural parameters

Single-knitted fabrics Double-knitted fabrics

Greige Bleached Greige Bleached

Fabric thickness 0.298NS 0.821a 0.416NS 0.600a

Fabric weight 0.702a 0.949a 0.242NS 0.958a

Stitch density 0.813a 0.142NS 0.044NS 0.713a

Calculated Porosity 0.896a 0.246NS 0.546a 0.812a

aThe correlation with the UPF is significant at the 0.05 confidence level.NSThe correlation with the UPF is not significant at the 0.05 confidence level.




Fabric weight of double-knitted cotton fabrics

Similarly, there are significant differences in fabric

weight among the six double-knit structures



between structure and bleaching (F 5,24 ¼ 269.254, p 0.05). Knit structure (partial eta squared ¼ 0.99),


action between knit structures and bleaching (partial

eta squared ¼ 0.982) have large effect sizes. The overall

fabric weights of double-knitted fabric specimens are

shown in Figure 7(b) and most of them increased

after bleaching except the full cardigan (t17 ¼ 3.93,

p 0.05, two-tailed). This may be because of the loss

of fibrous material from the full cardigan during the

scouring and bleaching process resulting in weight

loss: further investigation is required in the future.

From the results of the post-hoc test, the greige inter-

lock (Mean ¼ 298.11, SD ¼ 1.29) and greige 1 1rib

(Mean ¼ 250.57, SD ¼ 2.76) have the largest difference

in fabric weight, as well as the bleached interlock

(Mean ¼ 430.14, SD ¼ 5.26) and bleached full cardigan

(Mean ¼ 241.66, SD ¼ 3.27). The bleached interlock

and Milano have relatively higher fabric weight than

the bleached 1 1 rib and cardigan because of the com-

pact structures where yarns are closely packed together

resulting in higher fabric weight.

From the results of correlation analysis shown in

Table 2, positive correlations are found between the

UPF and fabric weight of the greige single-knitted fab-

rics (r ¼ 0.702, p 0.05), bleached single-knitted fabrics(r ¼ 0.949, p 0.05) and the bleached double-knitted

fabrics (r ¼ 0.958, p 0.05). The strength of these posi-

tive correlations is large (r ¼ 0.50–1.0) according to

Cohen’s suggestion.55 With higher fabric weight, the

UPF of greige and bleached single-knitted fabrics and

bleached double-knitted fabrics can be enhanced.

However, there is insignificant correlation between the

UPF and fabric weight of greige double-knitted fabrics

(r ¼ 0.242, p ¼ 0.334). This can be confirmed with

Figures 5(b) and 7(b), which show that even though

the greige double-knitted fabrics have similar fabric

weights, their UPF results are quite distinct. The nat-

ural pigments and impurities in greige fabrics may be

the reason for the insignificant correlation resulted.

Double-knitted fabrics have a relatively more compact

structure than the single-knitted fabrics and there are

natural pigments and impurities encompassed in the

greige double-knitted fabrics. The fibrous material

and the natural pigments already absorb the UVR

effectively; therefore, variation in the fabric weight

does not have a great impact on the UPF. Fabrics

with similar weights but different colors or fiber con-

tents may exhibit very distinct UV protective ability,

which suggested that fabric weight is not the only

factor in explaining the UV protection of fabric.

Stitch density of single-knitted cotton fabrics

Significant differences in fabric stitch density are found

among the four single-knit structures (F 3,16 ¼ 308.31, p 0.05), greige and bleached fabrics (F 1,16 ¼ 425.66,

p 0.05) and the interaction between knit structures

and bleaching that influenced the stitch density

(F 3,16 ¼ 9.75, p 0.05), as shown in Table 1. All of

their effect sizes are large; knit structures (partial eta

squared ¼ 0.98) and bleaching (partial eta

squared ¼ 0.96) have similar effect size and both are

larger than the interaction (partial eta squared ¼ 0.65).

The shrinkage caused by scouring and bleaching

brought a significant increase in stitch density, as

shown in Figure 8(a) (t11 ¼ 11.11, p 0.05, two-

tailed). The results of the post-hoc test indicate that

the largest differences in stitch density are found

between the greige all knit (Mean ¼ 80.61, SD ¼ 1.06)

and greige knit & tuck (Mean ¼ 39.22, SD ¼ 3.03) and

between the bleached all knit (Mean ¼ 107.13,

SD ¼ 4.55) and bleached knit & tuck (Mean ¼ 53.01,

SD ¼ 3.49). However, insignificant differences in stitch

density are found between the bleached all knit and

bleached knit & miss (25%), as well as the bleached

knit & miss (25%) and bleached knit & miss (50%).

The knit & tuck has the lowest stitch density, while

the other three single-knit structures have a similar

stitch density because the tuck stitch widens the fabric

and results in fewer wales per length.

Stitch density of double-knitted cotton fabrics

Likewise, the results of the ANOVA in Table 1 show

that the stitch density of double-knitted fabrics differs

significantly in the knit structures (F 5,24 ¼ 448.017,

p 0.05), greige and bleached fabrics (F 1,24 ¼ 77.63,

p 0.05) and also there is an interaction between struc-

tures and bleaching that influenced the stitch density

(F 5,24 ¼ 14.214, p 0.05). The effect sizes of structures

(partial eta squared ¼ 0.989), bleaching (partial eta

squared ¼ 0.764) and the interaction (partial eta

squared ¼ 0.748) are large; the knit structure has

greater impact on stitch density than bleaching. Most

of the double-knit structures studied show a significant

increase in stitch density after bleaching (t17 ¼ 3.99,

p 0.05, two-tailed), except the half cardigan with an

insignificant decrease in stitch density. The cardigan

structures do not have obvious variation in stitch dens-

ity after bleaching when compared to the other four

double-knit structures, as shown in the micrographs

in Figure 4. The structure with tuck stitches is

generally less extensible in nature particularly to the

Wong et al. 695



double-knitted fabric, which has a compact fabric

structure. The results of the post-hoc test indicate the

largest differences in stitch density are found between

the greige half Milano (Mean ¼ 99.48, SD ¼ 1.15)

and greige full cardigan (Mean ¼ 30.95, SD ¼ 4.69),

and also between the bleached half Milano

(Mean ¼ 104.21, SD ¼ 4.35) and bleached full cardigan(Mean ¼ 30.93, SD ¼ 2.15). Although the half Milano

structure possesses the highest stitch density and there

are insignificant differences in stitch density among the

half Milano, full Milano and interlock, the UPFs

among them are quite different: the interlock has the

highest UPF among the six double-knit structures.

The results of the correlation analysis shown in

Table 2 reveal that significant positive correlations are

only found in the greige single-knitted fabrics

(r ¼ 0.813, p 0.05) and bleached double-knitted fab-

rics (r ¼ 0.713, p 0.05). These positive correlations

indicate the UV protection will be enhanced when the

stitch density of greige single-knitted fabrics and

bleached double-knitted fabrics increased. The greige

single-knitted fabrics have natural pigments and impu-

rities acting as natural UV absorbers and more UVR

can be absorbed when the natural UV absorbers in the

yarn are packed closer together. However, the greige

double-knitted fabrics already have a dense fabric

structure together with natural UV absorbers for block-

ing the UVR; therefore, the increase in stitch density of

greige double-knitted fabrics will not bring significant

impact to the UPF. After bleaching, the natural UV

absorbers were removed and therefore the fabric struc-

ture of bleached double-knitted fabrics becomes a moreparamount factor in explaining the variation in UPF

when the stitch density increases.

Porosity of single-knitted cotton fabrics

Porosity was found to be a major indicator for UV

protection of a fabric.8,41–45 The fabric construction

influences the pore size, pore distribution, pore con-

nectivity and total pore volume, and all of these proper-

ties of the macro-pore are important in determining

UVR transmission of a fabric.56 By studying the por-

osity of fabric, the fabric construction can be con-

sidered in a three-dimensional approach with the

structural parameters, thickness and weight (areal dens-

ity), fiber density and the void spaces within the fabric

layer included.

From the results of the ANOVA shown in Table 1, it

can be found that a statistically significant difference in

porosity is found among the four single-knit structures

(F 3,16 ¼ 45.958, p 0.05), but not between the greige

and bleached single-knitted fabrics (F 1,16 ¼ 0.292,

p ¼ 0.596). This reveals that bleaching does not have a

conspicuous impact on the porosity of single-knitted

fabrics, although there is an interaction between bleach-

ing and the single-knit structure (F 3,16 ¼ 7.423,

p 0.05). The effect size of knit structure (partial eta

squared ¼ 0.896) is greater than that of bleaching (par-

tial eta squared ¼ 0.018) and also the interaction

between knit structures and bleaching (partial eta

squared ¼ 0.582). There are insignificant increases inporosity for the single-knitted fabrics after bleaching

that are contrary to the previous structural parameters

studied (t11 ¼ 0.34, p ¼ 0.737, two-tailed), as shown in

Figure 9(a). Although there are significant changes in

fabric thickness and fabric weight for the single-knitted

fabrics, porosity has less variation after bleaching

because the shrinkage of fabrics in scouring and bleach-

ing caused increase in fabric weight and thickness

simultaneously.

The results of the post-hoc test indicate that the greige

knit & tuck (Mean ¼ 89.35, SD ¼ 0.11) and greige knit &

miss (25%) (Mean ¼ 86.97, SD ¼ 0.32) have the largest

difference in porosity, as well as the bleached knit & tuck

(Mean ¼ 88.42, SD ¼ 0.12) and bleached knit & miss

(25%) (Mean ¼ 87.29, SD ¼ 0.30). The porosities

among the other three structures, all knit, knit & miss

(25%) and knit & miss (50%), are not significantly dif-

ferent from each other in both greige and bleached

stages. The bleached and greige knit & tuck have

higher porosities than the other three single-knit struc-

tures because the presence of tuck stitches increases the

porosity of fabric due to the unique formation of a tuck

loop. Since a tuck stitch is formed when a needle takes a

new loop without clearing the previously formed loop

(held loop), the held loop together with the loop that joins (tuck loop) are accumulated on the needles and

eventually give a bulkier structure to fabrics with more

void space within the fabric layer. Although the four

single-knit structures have quite similar fabric thickness

and weight, they differ in stitch density and porosity

because of their distinct fabric structures. A fabric with

higher porosity represents its fabric structure, encom-

passing more void spaces or fabric pores; in other

words, it is a rather porous structure. The knit & tuck

structure is obviously more porous than the other three

single-knit structures, as shown in Figure 4, and also

reflects the result of lower stitch density, even resembling

the fabric weight and thickness. Fabric porosity is a key

factor for UVR transmission, as the incident light can

pass through the fabric pore directly.42 Therefore, the

knit & tuck fabric provides more void spaces for the

transmission of UVR through the fabric, resulting in a

lower UPF than other single-knit structures.

Porosity of double-knitted cotton fabrics

Double-knitted fabrics have significant differences in

porosity among the six double-knit structures






between structure and bleaching (F 5,24 ¼ 24.843,

p 0.05). The effect size of the double-knit structure

(partial eta squared ¼ 0.95) is larger than bleaching

(partial eta squared ¼ 0.786), as well as the interaction

between knit structures and bleaching (partial etasquared ¼ 0.838). Most of the double-knit structures

have significantly increased in porosity after bleaching,

as shown in Figure 9(b) (t17 ¼ 3.35, p 0.05, two-

tailed), but there is no remarkable variation in porosity

for half Milano fabrics after bleaching. The results of

the post-hoc test indicate there are the largest differ-

ences in the porosity between the greige half cardigan

(Mean ¼ 88.51, SD ¼ 0.66) and greige interlock

(Mean ¼ 85.66, SD ¼ 0.12), and also between the

bleached full cardigan (Mean ¼ 91.2, SD ¼ 0.08) and

bleached interlock (Mean ¼ 85.87, SD ¼ 0.25).

Similarly, the cardigan structures comprised of tuck

stitches have higher porosity than the other double-

knit structures. Tuck stitches create more void space

for the fabrics by pushing the neighboring wales further

apart, whereas miss stitches pull the wales closer

together, which diminishes the void volume contributed

by the interstices between the yarns. The interlock and

Milano fabrics obtain the lower porosity in both greige

and bleached stages, which conformed to the results of

higher UPF among the six double-knit structures.

Significant negative correlations between the UPF

and porosity are found in the greige single-knitted fab-

rics (r ¼ 0.896, p 0.05) and bleached double-knitted

fabrics (r ¼ 0.812, p 0.05), while the correlationbetween the UPF and porosity for the bleached

single-knitted fabrics is insignificant (r ¼ 0.246, NS)

as indicated in Table 2. The negative correlations

obtained for both greige single-knitted fabrics and

bleached double-knitted fabrics have large strength

according to Cohen’s suggestion,55 and the results

agree with previous results and discussion about the

presence of tuck stitches in the fabric structures leading

to an increase in porosity but reduction in UPF.

Although UPF and porosity of the greige double-

knitted fabrics are found to be positively correlated

(r ¼ 0.546, p 0.05), the strength of this correlation is

not as large as the previous negative correlations found.

Other factors may contribute to the UPF of the greige

double-knitted fabrics, such as the beige color of greige

fabric specimens, which absorbs the UVR. Deliberation

is required in the future works for exploring other

factors.

Conclusions

The UPFs are statistically different among various

fabric constructions with knit, tuck and miss stitches.

Generally, the fabrics incorporated with miss stitches

possess higher UPFs than fabrics with tuck stitches.

The greige single-knitted fabrics obtain higher UPFs

after bleaching, whereas the UPF of the double-knitted

fabrics decreased after bleaching. The effect size of

bleaching for the double-knitted fabrics is greater

than that for the single-knitted fabrics; therefore, knitstructures play a more important role in the variance of

the UPF than bleaching for single-knitted fabrics. It is

assumed that shrinkage of the single-knitted fabrics

caused by bleaching has a notable influence on the

UPF when compared with the effect of bleaching,

which removes the natural pigments and impurities.

In addition, the knit & miss (50%) fabrics and interlock

fabrics possess the highest UPF among the single-knit

and double-knit structures studied, respectively. The

micrographs provide a clear illustration of fabric con-

struction and fabric pores among different knit struc-

tures, which assist the explication of the effect of the

knit, tuck and miss stitches on UVR transmission.

Fabrics with high fabric thickness and weight do not

always give better UV protection. This is proven by the

knit & tuck structure, which has a lower stitch density

and higher porosity but similar fabric weight and thick-

ness to the other single-knit structures. Fabrics with

tuck stitches have larger fabric pores than the other

fabrics, which allow more UVR to pass through the

fabric directly.

The results of the ANOVA indicate that fabric

thickness, fabric weight and stitch density for both

single-knitted fabrics and double-knitted fabrics are sig-

nificantly influenced by bleaching and knit structureswith large effect sizes, as well as the porosity of

double-knitted fabrics. However, the porosity of

single-knitted fabrics is significantly affected by knit

structures, but insignificantly influenced by bleaching.

In addition, the results of correlation analysis reveal

that fabric thickness is positively correlated to UPF

for the bleached single- and double-knitted fabrics,

while fabric weight is positively correlated to UPF for

the greige and bleached single-knitted fabrics, as well as

bleached double-knitted fabrics. Nonetheless, the UPF

of double-knitted fabrics decreased while the fabric

thickness increased after bleaching. This indicates that

bleaching has a greater impact on UPF than fabric

shrinkage for double-knitted fabrics by removing the

natural pigments and impurities acting as natural UV

absorbers. Although various knit structures have simi-

lar fabric weight and thickness, the results of UPF and

stitch density are quite contrasting. Moreover, the fab-

rics with tuck stitches possess relatively higher fabric

porosity but lower UPF than the other structures for

both single- and double-knitted fabrics, because tuck

stitches give a bulkier structure to fabrics with more

void space for UVR transmission. This conforms to

Wong et al. 697



the negative correlation between UPF and porosity of

the greige single-knitted fabrics and the bleached

double-knitted fabrics.

Most of the single and double-knitted fabrics studied

do not have a high UPF that can be classified to be UV

protective (below UPF 15), except the greige double-

knitted fabrics with very good protection (UPF 25–39)and the bleached Interlock fabrics with good UV pro-

tection (UPF 15–24).35 Nevertheless, this paper pre-

sents a precursory study using cotton as the raw

material to investigate the impact of knit structures

and their respective structural parameters upon the

UPF. The project aimed to provide textile scientists

and technologists with a comprehensive and valuable

database for manufacturing UV protective light-weight

knitwear. Therefore, other factors contributing to the

UPF of knitted fabrics, such as fiber, color, wetness,

stretchability, chemical treatments or additives applied

on fabrics, as well as the relationships between these

factors and the UPF, will be researched in the future.

The results will enable textile manufacturers, designers

and users to select the most effective combinations of

variables from a range of fibers, fabric constructions

and textile wet processing agents for the production

of UV protective knitwear, and this value-added infor-

mation will bring significant benefits to the world wide

textile and clothing industry.

Funding

This work was supported in part by the General Research

Fund (grant number A-SA21) from the University Grants

Committee, Hong Kong and The Hong Kong PolytechnicUniversity, Hong Kong.

Acknowledgement

The authors would like to thank Prof. Ron Postle of the

University of New South Wales for his help and advice on

this research.

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