Stretchable denim: A review
By: Manjunath Burji, P.V. Kadole & Sandip Patil
Denim is one of the cotton fabrics used for manufacturing jeans. It has become an
evergreen favourite of every individual worldwide irrespective of age, gender, season,
occasion and fashion. The textile industry has produced more indigo denim than any
other woven fabric. The denim fabric is bluer on the surface, being warp-face. The
weft is left undyed which makes the fabric appear almost white on the reverse. The
reasons for the unmatched success of denim are durability, comfort, feel, appearance
and versatility. Now, denim trends are modified according to customer's
requirements to improve the quality of the fabric. Stretchable denims are more
popular than regular denim, because of their elasticity and fit.
There are two categories of stretch denim, based on the degree of stretchability. They
are, power or action stretch and comfort stretch. Power or action stretch provides a
fabric with high degree of extensibility and quick recovery. The stretch factor
generally ranges from at least 30-60 per cent or more with no greater than 5- 6 per
cent recovery loss. Comfort stretch alludes to fabric with less than 30 per cent stretch
factor and no greater than 2-5 per cent recovery loss.
Raw material for denim
The warp and weft most used is open-end (rotor spun). Now machine manufacturers
install a new device to the OE machine which can produce a slub effect in yarn with
predetermined thickness and spacing between two slubs. This yarn looks better than
Elastane yarns meet customer requirements of comfort, stretchability and
appearance, so that again new trends are developed in denims using elastane yarns
in the weft. Poly-lycra air-covered yarn and cotton-lycra core-covered yarn are
popularly used in denims.
The fibre-forming substance is a long-chain synthetic polymer comprised of at least
85 per cent of segmented polyurethane. Spandex is synthetic fibre known for its
elasticity and stretchability. It is stronger and more durable than rubber.
Spandex fibres are manufactured using solution dry spinning method and drawn out
to produce a long fibre. The most commonly used methods are the solution dryspinning that produces over 90 per cent of the world's spandex fibre.
Process involved in stretchable
Manufacturing process of weft way
stretch denim is:
Figure 1 Value chain of stretchable denim
Production of core-spun and cover-cover elastic yarn
Elastane yarn is produced on ring frame machine, rotor spinner and air vortex
machine with special attachment for spandex feeding system. Using special control
device to control spandex stretch, tenacity and drawing. In above techniques,
spandex is put at the centre and surrounded by other fibers. Polyester, nylon, rayon
and cotton are the more popular fibres used to cover spandex monofilament yarn.
Winding is the intermediate process between spinning and weaving. Lengths of yarn
are wound on a cone or spool for weaving. These cones are used to make warp beam
The last phase of yarn production is the winding process. Here the cops produced by
ring machines are spliced (joined) together and transformed into the bobbin format
of specific length. Splicing is the important process to improve productivity. There
are many types of splicing: thermos splicing, air splicing and knotting. The type of
splicer used depends upon the fibre type and further application of yarn. The sensors
monitor the yarn surface throughout the length of yarn and they remove faults in the
yarn like unevenness. Yarn spinning is completed by winding.
In general terms, warping is transferring many yarns from a creel of single-end
packages forming a parallel sheet of yarns wound onto a beam or a section beam. The
warp beam that is installed on the weaving machine is called the weaver's beam. A
weaver's beam can contain several thousand ends and for different reasons it is
rarely produced in one operation.
There are four types of warping:
Indirect or Sectional Warping
Sucker Muller (hacoba) sectional warping type of machine is one of the most popular
machines for warping. The section beam is tapered at one end. Warp yarn is wound
on the beam in sections, starting with the tapered end of the beam. In each section,
there are many threads that traverse together slowly throughout the length of each
section. The last section of tapered threads on warping beam keeps threads stable. It
is important that each layer on the beam contains the same number of yarns.
Machine parameters are speed 700mpm, warping width 1500mm and warp beam
pressure 2000N with creel capacity 432. The number of each section depends upon
the creel capacity
Dyeing of warp sheet
Dye is applied on the weaver's beam before it gets to the loom. There are two ways of
Dyeing and sizing
Rope dyeing is the most popular dyeing methods for denim fabric. This gives good
results of dye shade on warp sheet. For most denim warps, there is no need to size
after dyeing because of the heavy count, so there is less warp breakages on loom.
Sucker Muller dyeing cum sizing machine is very efficient for count range between
10s Ne to 20s Ne. Both the dyeing and sizing operations are done in a single stage.
Shade percentage depends upon the speed of machine and concentration of dye
solution. According to requirement of shade percentage, for better shade percentage
machine speed kept at 30mpm (0.63 shade percentage for indigo dye) with yarn
through put 4.45 kg/min. After drying of warp sheet, the warp sheet is immersed in
size-paste bath for adding additional strength to warps and coating to avoid the
abrasion of threads on loom during weaving. Parameters are refractive index 10
(measurement of solid content), viscosity of 20, size pick-up 70-80 per cent and size
add-on 7-8 per cent for better performance on loom during weaving.
● Sulphur dye
Sulphur dyes are widely used on cotton because they are economical. They have good
to excellent wash-fastness and good light-fastness in dark shades. Light fastness of
pale shades is poor.
● Vat dye
Vat dyes are mainly applied on cellulosic fibres, but some can be applied to protein
fibres. Indigo is a special case in the vat dye class. Indigo is attractive for its pleasing
blue colour and for the unique fading characteristics of garment dyed with it. Vat
dyes are characterised by the presence of a ketone group. Vat dyes in ketone form are
There are many ways to produce elastane fabric by many fabric forming technologies.
Popularly, it is produced by knitting and weaving technologies. Knitted fabric is more
stretchable than woven fabric because of the loop structure. Elasticity of fabric is
much lower in both the cases than that of the elastane yarn because of the restriction
of the hard fibre structure. Stress and strain curve combined shows the elastic power
of the fibre and the effect of the hard fibre assembly recovering from compression.
Elastane yarns are more efficient in sports and comfort application. It gives sufficient
elastic properties to the fabric even with 2-3 per cent of elastane.
Interlacement between warp sheet and weft yarn is known as weaving. There is a
wide range of looms being used, right from the simplest handloom to the most
sophisticated loom. For denim fabric especially 1/2, 2/2, 3/1 types of twill weaves are
used for fabric construction. It is easy to weave on shuttles loom with better weaving
efficiency. Rapier is one of the best and popular machines for weaving of 10s Ne-20s
Ne warps and elastane weft for weaving stretchable denim.
Heat setting of fabric
Heat setting is the more important stage to keep the fabric width constant
throughout the fabric to avoid further shrinkage in finishing stage. At this stage,
shrinkage of fabric width and length are in our hand. We have to keep it according to
garment requirement. Recommended temperature of six chambers are 1750c and
speed of around 40 meters/min, for stretchable denim fabric.
The Stenter is a gas-fired oven, with the fabric passing through on a chain drive, held
in place by pins. Air is circulated above and below the fabric before being exhausted
into the atmosphere. As well as for drying processes, the stenter is used for pulling
the fabric to width, chemical finishing and heat setting and curing. It is versatile
equipment. Modern stenters are designed with improved air circulation, which helps
to improve drying, and with integrated heat recovery and environmental abatement
It is a process done to fibre, yarns and fabric causing them to change in appearance,
texture and performance. The term 'finishing' covers all those treatments that serve
to impart to the textile the desired end-use properties. These can include properties
relating to visual effect, handle and special characteristics such as waterproofing and
non-flammability. Finishing treatment is done to achieve the ultimate customer
requirements. These are mostly value added processes.
Type of finishing:
In case of stretchable fabric, normal finishing is suitable. Keep the temperature at
1000c-1100c and warp shrinkage approximately at 10 per cent.
Following are the tests carried for elastic fabric
Table 1: Yarn testing
Tensile testing of normal yarn
Elastic property (CRE type testing machine)
ASTM D2256 & ASTM
Table 2: Fabric testing
Breaking Strength (CRT type machine)
Moisture vapor transfer rate
AATCC test method 135
Elastane fabric is more suitable for comfort than non-elastane fabric. Elastane fabric
is used in athletics and sports and may improve performance in sports like cycling
and swimming. They are also important for inner wear. This type of fabric enables
freedom of body movement by reducing the fabric resistance to body stretch. Drastic
differences between skin and fabric movements result in restrictions of movements
to the wearer.
Elastic property of fabric gives it outstanding performance welcomed by consumers.
From a debut in sports and leisure garments it is now becoming the standard for
working apparel and in denim, the universal clothing fabric. Elastic fabric gives much
better properties like wear comfort, crease resistance, durability, drape and handle
than regular fabric.
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Textile Industry & Trade Journal January-February 1999 pages 43-47.
2. Ashwin Thakkar, "Some aspects of producing stretch denim fabric," Indian
Textile Journal, November 2012 pages 32-37.
3. Scott c. Wagner, Technical bulletin on denim fabric manufacturing, pages 42 and
4. A Merrow Monograph, Elastomeric Fibers by R. Meredith, Book, pages 9-36
5. Dorlastan.com (20-08-2008).
6. Gajanan Bhat, Subhash Chanda & Simon Yakopson, "Thermal Properties of
Elastic Faibres," Thermochimica Acta, 2001 page 367.
7. Preston University Report On Denim Manufacturing.
8. "Annual book of ASTM standards" section 7 vol. 7.2, year 2011.
9. M. Senthilkumar, N.Anbumani, J Hayavadana, "Elastane Fabric - A Tool for
Stretch Application in Sports," Indian Journal of Fibre & Textile Research,
September 2011 Vol 36 page 300-307.
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Publication, Cambridge UK), 2005 Chapter 10 pages 205-230.