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Acknowledgments
The editors gratefully acknowledge information supplied by Polywarm Products Ltd and the
considerable assistance and advice offered by David Houston of Daimor Sleeping Bags.
Cover picture courtesy of Daimor Sleeping Bags.
I l f i l l R l l U
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Alan Stancliffe was sponsored by the British Plastics Federation The Institute of Materials
British Plastics Training Association and the Polymer and Rubber Association.
The material was produced as part of the polymer industry education project at the
Chemical Industry Education Centre
Department of Chemistry
University of York
Heslington
YorkY015DD
Telephone (01904) 432523
ditors
Judy Jones
Alan Stan cliffe
With contributions from Gill Thomas - CIEC information officer
© Held by the University of York
Published 1995
ISBN: 1853427055
The copyright holders waive the copyright on the material which follows to the extent that
teachers may reproduce this material for use with their pupils in the establishment for which
the material was purchased, but for all other purposes permission to reproduce any of this
material in any form must be obtained from the University of York. The material may not be
duplicated for lending, hire or sale.
ii
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ONT NTS
Foreword
Resources
Product design and development
Activities 1, 2 and 3
Analysis of general functional requirements for sleeping bags
Materials selection in product design
Development of a new product
Development of a new sleeping bag design
Factors influencing the development of a new product
Materials used in sleeping bags
Environmental extension activity
The manufacture of sleeping bags
Student sheets for activities 1-3
Information sheet for activity 1
Information sheets (a) to (g) for activity 3
OHP1 a) Factors influencing the development of a new product
b) New product path
a) The construction of sleeping bags
b) Stitch constructions used with synthetic fillings
0HP2
iii
Page
V
V
12
2
3
3
4
4
5
5
AI-A3.2
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oreword
This package has been produced as a result of requests from design and
technology teachers. They asked for case study resources which demonstrate
the processes involved in industrial product design and selection of materials
for manufacture. It consists of a teachers' booklet and separate student work
sheets.
The package is intended to provide background information for use by
teachers and 14-16 year old students involved with design and technology
courses which contain elements of product design. It could also be made
suitable for younger students and post sixteen (A-level, GNVQ students by
modifying the level of expected outcomes in the suggested activities.
Students carry out a critical investigation of the design and manufacture of
sleeping bags as a product analysis exercise. This will help students to
develop technological and scientific skills and understanding by exploring the
properties of fillings, cover materials and processes used in the design andmanufacture of sleeping bags.
The teaching notes deal with the different stages of market research and
product design in the sleeping bag industry, and with the selection of
appropriate materials and manufacturing processes. They also offer further
guidance on classroom management of the student activities and
investigations.
Separate student copy master sheets (AI-A3.2) are provided which contain
background information and suggestions for analysis and problem solving
activities. Additional information for activities 1 and 3 (yellow sheets) is also
appropriate for product analysis exercises which can be devised by the teacherto suit particular circumstances.
A second unit is available in the Making Use of Science and Technology
series, also published by the Chemical Industry Education Centre,which
contains scientific investigations based on the construction and properties of
materials of sleeping bags.
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Resources
Samples of materials for testing can be obtained from
Tor Outdoor Pursuits
42 Widnes Road
Widnes
WA86AL
Tel:01514242225
This company will sell small quantities of fabrics and fillings.
At the time of printing typical prices were:
Fillings
Hollofil insulation (DacronFF2H) width 150cm
170g £3~~0per metre
240g £4.5b per metre.
Quilted insulation width 150cm
80g £3.80 per metre
150g £4.40 per metre
Duck down £9.50 per 100g pack
Outer cover fabrics
Nevetex 110 polycotton
Width 150cm
£4.20 per metre
200 Nylon plain fabric
Width 150cm
£3.20 per metre
Pertex 4 woven microfibre fabricWidth 163cm
£4.50 per metre
Tor Outdoor Pursuits are happy to receive enquiries about their products, but ask that
a stamped addressed envelope be included for replies.
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Teaching Notes
Activity 1
This is a group discussion exercise using the information on student sheet A 1o
consider the factors which might influence the sleeping bag manufacturer'schoice of material. An additional information sheet for activity gives the relative
costs of common materials.
Activity 2
This is an exercise based on the market research stage of the design and
development cycle and is supported by student sheets A 2.1 and A 2.2. OHPI can
be used in a class discussion to help students formulate a structure for their
investigations. This activity could be carried out with students working in small
groups and might include the following:
• a survey of existing stock kept by local retail outlets to determinecurrent popular conditions of use, fashion and colour trends
• a survey to compare current costs to the customer
• a survey of use and preferences within the school population
• development of a marketing strategy from the information obtained
Activity
A teacher-led class discussion based on information on information sheets (a) to
(g) for activity 3, and OHP2 forms an introduction to this activity. It is an analysis
and investigative exercise designed to illustrate the considerations which are
involved with materials selection. Ideally it should be done with students
working in small mixed ability groups. This creates opportunities for students to
support each other in an exercise that is quite complex.
Using the information provided in information sheets (a) to (g), students are
required to list the functional requirements which apply to sleeping bags. They
must compare these requirements with the general properties and
characteristics of cover and filling materials, and fabrication construction
techniques. Samples of different cover, lining and filling materials can be
examined under a microscope (8x and 20x magnification) to observe the
characteristics described in the text of the student sheet. Groups can then be
assigned one of the following working conditions and asked to produce a short
report on the suitability of combinations of materials and fabrication structures
for use in the design and manufacture of appropriate sleeping bags.
i) summer low level camping in the UK
ii) a Himalayan trekking expedition
iii) a polar expedition
Reports can be produced in a written format, poster illustrations, verbal and/or
video presentations, to cater for a range of ability levels. There is no definitive
answer and a variety of acceptable solutions may be produced by the students. As
a concluding exercise, each group can present its final report to the whole class,
and compare and evaluate the different solutions offered.
The following sections demonstrate how the activities relate to the real world of
design.
1
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Background information
Analysis of general functional requirements for sleeping bags
Whilst many sleeping bags can be considered multi-functional, they are
generally designed for specific outdoor conditions such as winter camping,
mountaineering, summer walking expeditions or general travel. Therefore thefirst questions relating to functional requirements would normally be:
What is the primary use for the sleeping bag?
In which temperature range will the bag regularly be used?
In which other conditions will the bag commonly be used?
After considering these questions carefully a designer is in a position to look at
cover fabrics and filling materials for a particular sleeping bag. As with most
insulation, sleeping bags work by trapping and holding air as still as possible.
They use the body's heat to warm this air. The efficiency of a sleeping bag relates
to the amount of air it can trap; this is affected by the combination of filling
material, and the design and construction of the bag.
Materials selection in product design
When designers are considering which materials to select for a particular
product they normally liaise with a materials expert who advises on the
development process. There are two fundamental concepts which are considered
in the selection of materials. These are:
• materials must have properties which allow the designer
to produce a required effect
• the choice of material will influence the manufacturing
methods and vice-versa
Designers are not normally experts in, but are familiar with, materials and
manufacturing processes. Most designers build up a number of personal
contacts with specialists in materials science, manufacturers of processing
equipment and mould makers, and draw on their experience while seeking
solutions to problems.
There have been considerable developments in new materials over the past few
years and these have found applications in almost every field of design and
manufacture. This has made the process of material selection more complex for
designers. When selecting materials for specific products the designer must
consider which ones offer the best balance of properties. It is unlikely that any
material will meet the specifications perfectly and the usual compromises are
between desired performance and cost. Some of the main factors to be taken into
account are listed in student sheet Al, and a class discussion on materials
selection can be centred around this.
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Development of a new product
Analytical studies of industrial management and business performance
structures have identified three kinds of cycle times. These are time-to-market
(i.e. design and development), production time, and delivery time (order
processing). The first stage is the design 'and development cycle (or lead time).
In the sleeping bag industry this usually takes from 1 to 3 months. A diagram(New Product Path) is given in student sheet A 2.1 which illustrates the various
stages in this process. Student sheets A 2.1 and A 2.2 and the following notes can
be used together to form the basis of a class discussion of the design cycle involved
in the development of a new sleeping bag product.
Development of a new sleeping bag design
Typical working stages in the development of a new sleeping bag design are:
a) A marketing strategy is developed by:
• identifying the customers who will buy the sleeping bag;
• identifying the type of image the product range will project.
b) The designer is briefed and produces several concept proposals for
consideration by the project managers.
c) The designer develops the proposals approved by the project managers.
d) The designer produces bag shape outlines and pictures of the product in
three dimensional coloured images, possibly using Computer Aided
Design (CAD).
e) A prototype bag is commissioned, and further development considered.
f) Prototypes are tested for performance and quality and assessed forconsumer acceptability. Any necessary modifications are then made.
g) Designs are produced for a range of sizes, shapes (rectangular/tapered
mummy), fittings and colours as required by the marketing brief.
h) Tooling is organised in preparation for final production.
The aspects which influence a new sleeping bag design can also be grouped into
factors leading to production and factors controlling production. A diagram
(Factors related to production) is given in student sheet A 2.2 to show this.
According to commercial research, production time is the key to profitability.
The research has shown that companies who have managed to reduce production
cycle time by 50 have improved their return on investment by about 10 .
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nvironmental extension a£tivity
Synthetic fibres are now being produced from recycled materials. As an average
estimate, 35 recycled 2 litre PET (polyethylene terephthalate) bottles can provide
enough polyester fibre filling for 1 sleeping bag. An extension to a£tivity could
be to engage the students in a survey of existing sleeping bag products to
determine which ones use recycled materials and to suggest possible ways of
recycling old sleeping bags which have come to the end of their working life.
he manufacture of sleeping bags
Information sheets f and (g) outline the main stages of manufacturing a
sleeping bag and can be used as the basis of a class discussion. Note the labour
intensive nature of the processes involved.
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tivity
Materials selection in product design
Working in groups:
1. Discuss how the factors outlined below might influence a
manufacturer's choice of material for a sleeping bag.
2. Prepare a report of the major outcomes of your discussion to
present to the whole class.
When selecting materials for specific products the designer must consider
which one offers the best balance of properties. Some of the main factors to be
taken into account are:
• appropriateness for the manufacturing process and quantity
production (machining, moulding, extrusion, etc.)
• physical properties of the material (strength, hardness,
chemical resistance, etc.)
• material form (sheet, rod, strip, liquid, fibre, etc.)
• aesthetic considerations such as colour, texture, pattern
and shape
• environmental considerations such as weather resistance and
ease of recycling
• safety such as flammability and toxicity
• cost (there is an information sheet to help you) and availability
Note
When designers are considering which materials to select for a particularproduct they normally consult experts in materials whose advice will
influence the development process. Two of the main considerations are:
• The materials must have properties which allow the designer to
produce the required effect.
• The choice of material will influence the manufacturing
methods and vice-versa.
Student sheet Al
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Information sheet for activity 1
Properties and costs of some commonly used sleeping bag materials
Cover fabrics
Material Properties mass Costperm2
(g/m2)
Performance Proof lightweight, waterproof, tear 00 £2.70
resistant
Matrix breathable, durable, waterproof 150 £8.50
Taslan similar to matrix but heavier duty 170 £8.00
and more robust
Tactel Milair lightweight, breathable, waterproof 125 £9.00
Ski-tex breathable, shower proof 130 £4.00
Pertex ultralight, draws away body 54 £2.80
moisture
Ripstop fabric soft, light, shower proof, can retain 68 £2.00
down
Polycotton breathable, windproof and shower 120 £1.80
proof
Nevetex 110 strong, windproof and shower proof 110 £2.80
200 Nylon plain I strong, tear resistant, not proofed 200 £2.00fabric
1 . . _
Filling materials
Material Properties mass Costperm2
(g/m2)
K2 Fleece fabric wind proof, low water absorbency, 250 £7.80
dries easily, easy to sew
Polar fabric soft, good insulator, easy to sew, 400 £3.80
machine washable
Thinsulate good insulator 100 £3.50
Hollofil soft, compressible, low water 170 £2.50
retention, very good insulator- • -.
Duck down £64 for800gxcellent insulator, compressible. 800g
needed
fora 4
seasonsleeping
bag
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Activity 2
Development of a new product
The development of a new sleeping bag design will be influenced by the
following factors:
• consumer requirements
• fashion and colour trends• demands of retailers and distributors
• society and environmental pressures
• properties of materials• technical aspects of manufacturing processes
Carry out a survey of existing sleeping bags in order to develop a marketing
strategy for a new product line. Your market research should investigate the
following:
• consumer attitudes and preferences
• an examination of existing cover styles, constructions
and fillings
• current costs to the consumer
Sleeping bag design involves the following two aspects:
• designs for the fabrication structure of the cover• selection of the most appropriate material for the filling
The design and development cycle (or lead time) for a new product in the
sleeping bag industry usually takes from 1 to 3 months. The diagram below
illustrates the various stages of this process.
CUSTOMER
MACH IN ISTS
PROTOTYPE
\MATER IALS
FABR ICAT ION
STRUCTURE
M AR KE T R ES EA RC H
\CONCEPT
DESIGN
/
New product path
Student sheet A 2.1
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1
The aspects which influence a new sleeping bag design can
be grouped into factors leading to production and factors
controlling production. These are shown below.
Factors Related to Production
2
Student sheet A 2.2
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Activity
Characteristics ofmateria1s used in sleeping bags
1. List the desired properties of materials used in the manufacture
of sleeping bags.
2. Examine the functional requirements for sleeping bags given on
student sheet A 3.2.
3. Compare these aspects with the general list of properties you have
identified. You could examine some of the available materialsunder a microscope using 8x and 20x magnification to help.
4. Use information sheets (a) - g to help you select appropriate
materials and construction techniques which will be suitable for
producing cost effective sleeping bags to be used under one of the
following conditions:
• summer low level camping in the UK
• a Himalayan trekking expedition
• a polar expedition
Note
Designers now use a range of natural and synthetic cover fabrics and filling
materials for sleeping bag design. Sleeping bags do not have to be thick to be
warm. It is the types of filling and stitching construction used in the cover
fabric which produce the required thermal insulation' properties. It is easy to
adjust the characteristics of sleeping bags to suit specific working conditions
using various permutations of cover fabric, filler material and stitching
construction.
Student sheet A 3.1
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General functional requirements for sleeping bags
1.Weightand bulk:if sleeping bags are heavy or bulky, they
will be more difficult to carry, so a light weight material,
which retains its elasticity after compression, is an
advantage.
2. Toughness: sleeping bags should be capable of withstanding rough
treatment both in use and when folded for transit and storage (crush and
compression factors).
3. Comfort and shape: most sleeping bags are tapered, rectangular,
or mummy shaped. They should be flexible enough to fit the body form,
non-constrictive, and allow movement during sleep.
4. Insulation: sleeping bags should possess thermal insulationproperties which are related to the conditions of use. Most manufacturers
classify sleeping bags according to the minimum comfort temperature(MCT). Bags should be designed to keep the occupant comfortably warm,
when used at this temperature, provided they are in a tent and using a
quality sleeping mat. The MCT classifications of use are as follows:
Class MCT Conditions
ISummer low level camping in the UK. Travel to
warm/temperate climates.
3 season mountain camping in the UK. Travel to coolerclimates.
3 I o o e 4 season camping in the UK. Alpine walking. Himalayan
trekking.
4Winter mountain camping in the UK. Alpine
-20oe mountaineering. Ski touring. Expeditions to all but the
highest, coldest places. ~-30oe Expeditions to the highest, coldest places (e.g. polar).
5. Waterproofing: some protection against contact with wet ground is
a desirable, though not an essential feature of sleeping bags.6. Drying time: sleeping bags should be capable of drying quickly.
7. Tear resistance: good quality sleeping bags use ripstop materials
to improve resistance to accidental tearing during use.
8. Flame retardation: this is a desirable property of the materials
used to manufacture sleeping bags.
9. Breathability: the ability of the materials to transfer perspiration vapour
from the skin to the outside of the fabric.
10. Zip together: some sleeping bags are designed to zip together
with other bags. This requires right and left handed versions.
Student sheet A 3.2
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Information sheet (a) for activity 3
Materials used in sleeping bags
Cover and lining fabrics'
Cover fabrics
Most sleeping bag manufacturers use a variety of polyester, cotton and nylon
fabrics for the cover material. This is because of the strength and lightweight
characteristics of these particular materials. The price and quality of a
sleeping bag depends on the quality of the materials used, as illustrated in the
following table.
Price range Material
Lower Polyester cotton quality nylon fabrics
Medium Ripstop quality nylon for added strength
Upper Pertex and ripstop quality Pertex
Pertex is a lightweight fabric made from tightly woven nylon microfibre
having almost 4000 filaments per square centimetre. It is water repellent,
windproof, breathable and dries very quickly when wet.
1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1
1 1 1 11 1 1 11 1 1 11 1 1 1 1 1 1 1 1 1 1 1 1 1 11 1 1 . •
The material comes in three
qualities, specified by weight as
follows:
Pertex
Pertex 4 (54g/m2)
Pertex 5 (69g/m2)
Pertex 6 (80g/m2)
A dense weave of microfine filaments
giving optimun pore size
Pertex 4 is matt, silky and extremely comfortable, making it an ideal high
quality sleeping bag cover fabric. For even higher quality and strength, with
increased resistance to tearing, there are two 'ripstop' versions, Pertex RS4and Pertex RS5. These are superfine, soft, immensely strong and were
originally developed for use in parachutes.
A hydrophobic coating of polyurethane can be applied to Pertex RS5 to
produce a completely waterproof yet breathable fabric. This fabric is more
expensive and known as Pertex 1000.
Ijning fabrics
Lining fabrics should be comfortable, soft and pleasant to feel. Sleeping bags
in the lower price range tend to use a brushed cotton polyester cotton or
viscose nylon for inner liners, in combination with an outer cover of polyester
cotton or nylon fabric. Sleeping bags in the upper price range tend to use
Pertex materials throughout, in particular Pertex 4 for linings.
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Information sheet (b)for activity 3
Materials used in sleeping bags
Filling materials- natural
Goose and duck down
Down is the lightest, warmest filling material available. However, it is
also the most expensive. Down should be used where lightweight, warmth
and lack of bulk are the priorities. The use of goose and duck down as a filling
material in sleeping bags is because of their durability, softness (cushioning
property), packability (resistance to compression damage) and loftcharacteristics. Down comes from the breast of the goose or duck and, in
contrast to the feathers from other areas, has no quill.
Loft is the ability of a filling material to maintain an even distribution when
enclosed by a cover fabric. Down is normally used with a small percentage offeather added which improves the loft quality and prevents the down from
clumping (gathering together in different areas of the sleeping bag).
Down filling is normally specified as the percentage of down followed by the
percentage of feather, e.g. 9 1 would represent 90 down with 10 of
feather. The best downs give a very high loft which in turn means more
warmth for less weight.
The insulating performance of a particular down is measured by its fill power.The fill power figure represents the volume (in cubic inches) occupied by 10z of
fully lofted down. Some examples of commonly used specifications are shown
below.
Fill type Fill power
85/15 DD 450
90/10 GD 550
90/10 DD 65 0
96/4 GD 70 0
DD duck down
GD goose down
Thermal insulation is then governed by a combination of the total mass and fillpower of any particular grade of down used in an individual sleeping bag.
e.g. A sleeping bag with a total mass of 1000g filled with 9 1 DD, will give a
higher thermal insulation than one with a total mass of 300g filled with
9 1 GD. This is because the first one has both greater mass and greater
fill power than the second.
A sleeping bag with 700g total weight of 96/4 GD will give a higher
thermal insulation than one with B O O g total weight of 9 1 GD. In thiscase, the first one is lighter, but has a fill power of 700, whereas the
second one, though slightly heavier, has a fill power of only 550.
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Information sheet (c) for activity 3
Materials used in sleeping bags
Filling materials- synthetic
Polyester fibres
Some characteristics which account for the use of polyester fibres as
filling materials for sleeping bags are as follows:
• toughness with good compactability and recovery
• less expensive than down• combines lightness and comfort (but heavier than down)
• is a thermoplastic with a natural feel• good thermal insulation properties and 'mildew resistant'
• dries much quicker than down• machine washable (usually at 40°C)
Polyester fibres used in sleeping bags can be either solid or hollow. Although
the hollow fibres are more expensive they trap more easily the thermal
insulation properties, and are softer. Sometimes a combination of solid and
hollow fibres are used to combine a lower cost with increased thermal
insulation, softness and resilience.
DACRON QlJALLOFIL 4 and 7 are all year round suitable polyester fibres with
a unique construction which combines the qualities of down with the easier
care and quicker drying characteristics of synthetic fillings. Each tiny fibre
incorporates four or seven air channels which trap air and provide excellent
loft and resilience. They are lighter in weight than other polyester fibres, have
20 more thermal resistance, and are used with stitch constructions normallyassociated with down filling. Although more expensive than other polyester
fillings they are a cheaper alternative to down.
Hollow fibres
QUALLOFILfibres
with 4 channel construction
QUALLOFILfibres
with 7 channel construction
Synthetic fillings are normally specified as the number of layers Batts of
filling followed by the mass in grams per square metre of each layer. Some
commonly used specifications for synthetic filling materials are:
1x 90 2x 125
Lx 180 2x 180
1x 270 2 x 270
170+ 1x 240
e.g. 1 x 90 means 1 filling layer Batt with a mass of 90g per square metre
and 2 x 125 means 2 filling layers Batts each with a mass of 125g per square
metre.
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Information sheet d for activity 3
The construction of sleeping bags
General construction
Sleeping bags comprise an outer cover, a filling, and an inner lining.
Outer cover
Stitch constructions used with down filling
Cover fabrics for use with down fillings are stitched into channel
constructions to allow maximum loft. Each independent channel is known asa baffle. The different arrangements illustrated below are used to help create
an even loft and a minimum of cold spots.
Box Wall Double Offset Box Wall
Slant Box Wall
(enhances overall insulation) V Baffles
Double Box Wall
(2 layers - increased thermal insulation)
The vertical side walls of the baffles are usually made from a lightweight
knitted fabric material, different from the cover and lining. Elasticated thread
is often used on high quality sleeping bags to sew the baffles in place. This
allows the fabric more flexibility to gently contour around the body shape and
thus reduce heat loss.
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Information sheet (e)for activity 3
Stitch constructions used with synthetic fjUing
Sewn Through constructions are used for the cover fabric with synthetic
fillings. Any line of through stitching creates cold spots which reduce the
insulation properties of the materials. To overcome this, Double Offset Layerconstructions can be used.
Sewn Through Double Offset Layers
Intermittent stitch patterns are other alternatives used to gain maximum loft
with minimum restriction. These consists of a series of short, alternate zigzaglines of stitching to hold the cover, filling and liner together and produce a
high efficiency of thermal insulation.
Intermittent Stitch
Construction
The combined materials are then overlock stitched around the edges, creating
a large internal air space.
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Information sheet t for activity 3
General manufacturing process
Shape
The shape for a particular sleeping bag is marked out on the materials and cut
by hand, using template patterns in a similar manner to that used in the
clothing industry.
Down filled sleeping bags
Pertex material is normally used for down filled bags. Prior to sewing, the
Pertex is 'down proofed' by passing through a set of rollers, one of which is
slightly heated. During this process the surface fibres on the inner side of the
material are fused together, which prevents the down from infiltrating the
fabric. This produces a 'wet look' appearance on the inside whilst leaving theouter surface of the Pertex in its attractive natural matt state.
The box channel constructions are individually sewn. using heavy duty sewing
machines. The down is weighed out and placed into the box channels by handin a still air environment (otherwise the down disperses into the air).
Fibre filled sleeping bags
Fibre preparationSynthetic fibres (which look like cotton wool) usually arrive at the factory in
bales. Fibres of different types and densities are mixed together to createspecific percentage blends for particular jobs. The blend mix is then passed
through a carding machine (as in the wool industry) to produce flat layered
sheets of different layer thicknesses.
To keep the fibres in place the carded sheets are either sprayed with a quick-
dry resin to bond the fibres on the outer surfaces, or special hot melt fibres are
included at the blending stage which melt when the layered sheets are passed
through an oven, creating an integral bond with the other fibres.
Resin spray
Fibre layered
sheet
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Information sheet g for activity 3
The outer cover material, fibre filling sheet and the lining material are
assembled together like a sandwich. The materials then pass through a
multi needle quilting machine which is set to stitch either straight lines or an
intermittent zigzag pattern.
Movement of needles for
intermittent stitch patterns
Sleeping bag
materials -~~ ~ Flatbed
To produce the intermittent stitch pattern, the needle heads descend and move
a fixed distance sideways in one direction, then lift and descend at anotherpoint before moving in the opposite direction to return to their original position,
as the materials pass through. This sequence repeats and the intermittentzigzag stitch pattern is built up. The process is computer controlled.
The materials are then manually overlock stitched around the edges using
heavy duty sewing machines.
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The Construction of Sleeping Bags
Stitch constructions used with Down filling
Box Wall Slant Box Wall
(enhances overall insulation)
V Baffles
Double Box Wall
(2 layers - increased thermal insulation)
Stitch constructions used with synthetic filling
[] iOO~:[E
ewn Through Double Offset Layers
OHP 2
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