Unit 2

Comfort properties of fibres

• Man-made fibers can not overcome the natural fibers.
• A garment with a blend of cotton and polyester is wrinkle
resilient and does not need to be ironed or will require less
ironing, while retaining much of the comfort provided by cotton.
• Polyester is strong and rayon has shininess. A fabric produced of
cotton/polyester/rayon offers durability, ultra-softness, and
excellent resilience .so that if wrinkled, the fabric bounces back.
• Spandex is stretchy and durable. Its blend with cotton is a very
good choice for sports cloth.
• Silk has luster and good drapability and does not crease easily.
Linen creases easily, but is strong and breathable. A fabric made
of a blend of silk and linen would not crease as readily and will
be shiny and drape better.
 Type of fiber
• The type of fiber is the most crucial specification
which determines important properties such as
strength, durability, handle, elasticity, dyeability,
luster, friction properties, moisture absorbance, heat
isolation and abrasion resistance; all the physical and
chemical properties of fibers and their end-products.
Fiber type is the most effective parameter in defining
the comfort of the end-product.
• Do not mean that natural fibers behave better in all
the comfort aspects with respect to synthetic fibers
• Fiber designing gives a powerful tool to the
producers to present their garments according
to environmental (warm or cold, humid or
dry), physiological, sensorial and any special
requirement of the applicant playing with
crucial fiber properties.
• Comfort is a term that is influenced by three
main properties of fibers: type, fineness and
length.
 Physical modification of fibers
• The cross-section of synthetic fibers depends
on the shape of the spinneret and the
behaviour of fiber dough when it comes out of
the spinneret and solidifies.
• Profiled fibers
• Microfibers
• Hollow fibers
 Profiled fibers

• Viscostar® trilobal cross-sectional cellulosic fibers are a

very good choice for nonwoven applications where
absorbency is the primary key parameter, such as
washing products, medical care, body protection
products, and so on.
• Unlike synthetic fibers, the diameter of cellulosic fibers
increases significantly in the wet state.
• Producing trilobal viscose fiber is a physical modification
to improve both bulkiness and water absorbency of
viscose fibers by 17% and 40% respectively.
 Microfibers

• Microfiber is defined as a staple fiber or filaments of

linear density approximately 1 dtex or less, and above
0.3 dtex.
• Acrylic, viscose and polypropylene are available for the
production of microfibers, polyester and polyamide are
the main source.
• Toray has introduced an ultra-fine polyester
microfiber with a linear density of filament of about
0.05 dtex. This may be called the finest synthetic fiber
so far produced commercially.
There are two techniques to produce microfibers:
• direct spinning (conventional POY spinning), and
• bi-component process (segment and island-in-sea type).
Different procedures produce microfibers:
1. Dissolved type
2. Split type
3. Direct spun type
4. Super-drawing technique
5. Sheath-core spinning method
6. Flash-spinning method
7. Solution flash-spinning
8. Emulsion-spinning method
9. Jet-spinning method
10. Centrifugal-spinning method
11. Turbulent forming method
• Microfibers have high strength properties, are very soft, have
luxurious hand with a silken or suede touch, extreme drapability,
ultra-fine linear density (less than 0.1 dtex/f) and are finer than the
most delicate silk.
• They are shrink resistant, washable, dry-cleanable, non-electrostatic
and are hypoallergenic, therefore they do not create problems for
those suffering from allergies.
• Anti-microbial agents help to protect the wearers from the dangers
of the bacteria that cause odor and mildew.
Microfibers are super-absorbent, absorbing over seven times their
weight in water and they dry in one-third of the time of ordinary
fibers. They insulate well against wind, rain and cold and
furthermore are environmentally friendly.
 Hollow fibers
• The cross-section of this fiber has a tubular
form that contains one or more holes.
 More resilience/recovery
 more bulky and fluffy
 higher heat insulation
 better cover
 lighter in weight
 higher absorption of water and perspiration
• Rounded, trilobal, triangular and squared
• Hollow fibers trap air, providing loft insulation
characteristics better than solid fibers, and when used in
carpet show less soil and dirt
• Hollow polypropylene microfibers are used because of
their high breathability, light weight and softness. These
fibers that are used for underwear are highly elastic and
have perfect temperature control and thermal isolation
• They have a pleasant handle, good water vapor
transmission, high thermal isolation and resistance,
lower fabric thickness and considerably lower pilling
extent
 Comfort properties of yarns
• The yarn structure is dependent primarily
upon the raw material, spinning process,
spinning unit, machine, machine settings,
twist, etc. The structure can be open or
closed; voluminous or compact; smooth or
rough or hairy; soft or hard; round or flat; thin
or thick, etc.
• Effect of yarn structure characteristics
• Linear density - Bending stiffness and compression
of the fabrics produced of yarns with higher linear
density are more than the fabrics with lower linear
density yarns.
• yarn diameter and fabric thickness decrease as
linear density decreases
• Increase in yarn fineness, yarn twist and providing a
less dense structure improves the air permeability
of the fabric
• fabrics produced of finer yarns have warmer filling
and lower thermal absorptivity. By increasing the
twist number of the yarns, water vapor
permeability and thermal absorptivity increase,
producing lower thermal resistance and cooler
feeling.
• A higher yarn twist number results in lower
wickability in such fabrics
• Effect of spinning technique
• Texturizing
Comfort properties of fabric structures
• woven(interlacing threads)
• knitted (interlocked loops)
• nonwoven (matted fibers)
• properties
• density, porosity, bulkiness, thickness,
structure and pattern.
• Fabric constructional parameters
- Thickness , weight per square meter,
pattern of weave and yarn count.
-Twill weave fabrics are tightly woven diagonal
line patterns that are strong, hard-wearing
and drape well.
They do not get dirty quickly, but if they get
dirty, it is more difficult to clean them.
• Satin does not show the diagonal lines as in
twill weave. It is flat, smooth and has a lustrous
surface, but is a weaker fabric. Warp yarns are
more visible on the right side of the fabric and
the floats are more susceptible to snagging. The
longer the float, the more likely it is to snag.
• Dense weave patterns, such as plain weave with
a high number of interlacings, reveal lower
shrinkage values.
• Whereas air permeability depends on yarn and
fabric structures and the shape and volume of
airflow channels in the fabric
• To explain the thermal insulation, warmness
and heaviness, fabric thickness and weight are
the most effective parameters
Finishing
• All finishing treatments affect the fabric
handle and comfort.
 Improving moisture management in
apparel
• Body temperature will be above that of the environment
and in order to maintain the heat balance between the
body and its surroundings, the body generates heat
through its metabolism.
• To maintain the body core temperature, these levels of
heat must be dissipated by dry and wet/latent heat
transfer.
• Dry heat transfer at the surface of the skin takes place by
means of conduction, convection and radiation .
• Wet heat transfer takes place through the evaporation of
moisture secreted on the skin
• Heat can flow from outside into the body in hot summer
weather, so reducing heat loss from the body.
• In extreme cold weather, the body loses heat rapidly,
leading to a loss of thermal balance.
• Lower levels of physical activity will lead to a fall in body
temperature due to a large reduction in heat generation
so the body heat must be conserved by increasing
insulation with suitable clothing, especially during cold
weather.
• Clothing is a good insulator for thermal conduction and
convection.
 Transport of perspiration
• Moisture from within the body is exuded
through the pores of the skin and evaporates
on reaching the outer surface. As it does so, it
draws the latent heat of evaporation from the
body which is needed to convert liquid water
to vapour. One gram of water takes 2260
joules of heat energy from the body in
evaporating.
• The water exuded through the skin appears
initially as a liquid which evaporates
immediately and forms moisture vapour.
• This vapour is then removed from the vicinity of
the body, either by convection or diffusion
through the pores of the clothing to the
outermost surface and is carried away by the air.
• The form of perspiration of which we are aware
is known as “sensible perspiration”.
• Sensible perspiration occurs in liquid form and wets the
clothing which is in contact with the skin when the ability of
the clothing to transport water vapour from the skin to the
outer environment is lower than the rate of perspiration.
• The water then condenses on the skin and must be
transported to the outer surface of the clothing.
Consequently, the comfort of a garment is greatly affected by
transport of moisture in vapour or liquid form through the
clothing to the outside.
• The liquid water in the pores will block the passage for the
diffusion of vapour and cause increased discomfort with the
onset of the condensation process.
 Perspiration depends on,
• Water vapour pressure
• Relative humidity of the micro climate
• Clothing and outside environment
• Absorption-desorption of the clothing
medium
• Heat of sorption
• The saturation/condensation of vapour
 Fundamentals of moisture transfer
between the human body and the
environment
• Moisture can be transferred in three ways: diffusion,
convection, and capillary transfer; and also by a
combination of these.
• Moisture diffusion through clothing
• Liquid water/sweat is secreted through the pores of
the skin. On evaporation, it takes latent heat from
the skin and in the process the skin is cooled.
• Sweating works well in a hot dry environment, but
evaporation of sweat becomes a problem in hot
humid climates.
• The process of water vapour transport from the
regions of higher water vapour pressure to the regions
of lower water vapour pressure is known as ‘diffusion’.
• Moisture transfer by convection and ventilation
• Forced convection is a mode of moisture transfer
which takes place when air flows over a moisture layer.
• The mass transfer in this process is controlled by the
difference in moisture concentration between the
surrounding atmosphere, the moisture source and the
convective mass transfer properties of the clothing.
 Ventilation
• Clothing micro-climate ventilation is critical to the
removal of sensible and latent heat from the body and
consequently has a major influence on the thermal
comfort.
• Ventilation causes a dynamic change of clothing
insulation due to wind penetration through the fabric or
ensemble openings, wearer displacement due to
motion causing a wind effect, and relative motion of the
clothed limbs with respect to their clothing cover.
• Ventilation causes a pumping effect, causing the
moisture vapour to move from the skin to the
atmosphere.
Liquid moisture transport by capillaries
• The transport mechanism of liquid water has a
significant impact on simultaneous heat and
mass transfer. Transport of liquid water across
clothing increases the thermal conductivity
and changes the heat transfer and moisture
absorption of the fibres.
 Mechanism of coupled heat and liquid moisture transport in
clothing

• The diffusion of water vapour in inter-fibre spaces

is slow for the properties of any given material
when compared to liquid water penetration of the
fabrics through capillary action.
• The process of water vapour diffusion into fibres
throughout the thickness of the fabric takes 2 to
2.5 minutes to reach a steady state, whereas liquid
water diffusion takes 0.1 to 1.6 seconds to reach
steady state, depending on the thickness (0.5 to 2.0
mm) of the fabric.
 Heat and moisture transfer in multi-layer
clothing
• Multi-layered clothing is used in cold and extreme
cold weather. The thermal resistance (dry) and
permeability to water vapour are important in these
weather conditions
• The thermal resistance for multi-layer fabrics is
much higher than the simple sum of individual
layers; this is mainly due to the formation of air
space between the fabric layers.
• This is especially true for a multi-layer clothing
system
Factors influencing moisture transport
 Porosity
 thickness of clothing
 complexity of pores
 fibre- diameter, shape, type (hydrophilic/hydrophobic)
 pore size distribution
 gradients of temperature
 water vapour pressure/concentration
 position of layers (hydrophilic/hydrophobic)
 ventilation
 atmospheric temperature and pressure.
 Improving moisture transport
• Perspiration on the skin should be evaporated on the skin
itself, utilising the latent heat of evaporation to cool the body.
The water vapour thus generated has to be diffused quickly
through the clothing.
• To avoid wetness of the skin and an associated loss of thermal
insulation, liquid water must be transported as quickly as
possible through the capillaries in the inner layer of clothing to
the next layer away from the skin.
• Again, from the point of view of keeping wetness of the skin to
a minimum, an inner layer made of hydrophobic fibres with
the necessary capillary forces is preferable as these do not
absorb moisture. The wicking rate of the inner layer may be
increased by treating it with a hydrophilic finish.
• Fibres with unique cross-sectional shapes such as
W-profile, grooved fibres of Cool max and 3-T
shaped have a large surface area which increases
the evaporation rate throughout the layer.
• In the case of summer clothing, the diameter of
pores in the outer layer should be less than that
in the inner layer, so as to exert a higher capillary
pressure which will draw the liquid from the
inner layer (i.e. one way wicking).
• Fleece used in the middle layers of cold
weather clothing has high porosity in order to
transport water vapour by diffusion.
• multi-layer clothing with Gore-Tex cover fabric
(three layered: woven + membrane + warp
knit) as its inner and outer layers, with the
middle layers consisting of either wool or
polyester, or both wool and polyester layers in
combination.
• The GORE-TEX® membrane is at the heart of all GORE-
TEX® products. Due to its micro porous structure it has
some amazing characteristics.
• The microscopic pores on the membrane are 20,000 times
smaller than a water droplet, which means water droplets
can’t pass through. The pores are 700 times larger than a
water vapour molecule which means perspiration passes
right through. This is what makes the membrane
breathable. The volume of air that passes through one
square meter of fabric in one second (l/m²sec) is 5.0 or
less, creating a truly windproof membrane.
 Clothing requirements for different
environmental conditions
• Hot and dry climate
• Hot and humid climate
• Cold weather
• Heat resistant clothing
Hot and dry climate
• In hot climates, the atmospheric temperature
is around 35–39 °C and may sometimes be
more than 45 °C.
• To be effective under these conditions, clothing
must possess good properties of ventilation which
permits moisture transfer by diffusion as well as
by forced convection and the fibre used should
retain minimal amounts of moisture if it is to
provide a cool feeling to the wearer in these
conditions.
• Hygroscopic fibres should be used and the fabric
structure must be very open to facilitate
ventilation.
 Hot and humid climate

• In tropical conditions, both the temperature and the

relative humidity of the atmosphere are very high,
around 70–75%.
• Under these conditions, the heat transfer processes are
ineffective in transmitting body heat to the atmosphere
and the low vapour pressure gradient between the skin
and the atmosphere reduces the rate of vapour diffusion
.
• These conditions require sweat to be absorbed by the
clothing nearest to the skin and passed through to the
outer layer of the fabric by a wicking action.
• A smooth inner fabric is preferable for coolness.
• Double knitted fabric made from wicking
polyester fibres (fine fibres of low modulus, with
a hydrophilic finish or grafted onto a hydrophilic
polymer or fibre with grooves) as an inner layer
with a texturised polyester on the outside will be
effective in drawing the perspiration by capillary
forces and will maximise the evaporation.
 Cold weather
• The insulation of clothing is the main factor in
maintaining a thermal balance in cold weather.
At very low temperatures, the temperature
gradient between skin and atmosphere is very
high and if the insulation properties of the
fabric are not high, the result will be a high
loss of heat from the skin to the atmosphere,
leading to a reduction in body core
temperature and ultimately to hypothermia.
• Cotton should be avoided for the base layer as it
becomes wet and clings to the body when the rate of
sweating increases. It takes a long time to dry and to
give a feeling of coolness. The sense of cold is
measured by thermal absorptivity which increases with
the thermal conductivity of the fibre and its density; in
cotton these values are higher than in synthetic fibres.
• Fine merino wool and wool/polyester fibres are well
suited to the base layer. These fibres can be treated so
as to wick away the liquid moisture from the skin.
• Polyester fleece ,pile fabrics are suitable for the
middle layer and provide the best insulation. Fine
fibres have less radiative loss. The thickness of the
middle layer is very important in enhancing insulation.
• In dry, cold weather, the outer layer must be
windproof for low air permeability, and waterproof in
wet weather. The outer layer should also be water-
repellent to minimise water pick-up. To permit
evaporation of water, the outer layer should have a
high water vapour permeability and low vapour
resistance.
 Heat resistant clothing
• Nomex and Nomex/FR rayon work-wear fabrics,
demonstrating that fabrics with fine fibres and a twill
weave have a higher moisture vapour buffering capacity.
• Clothing for fire-fighters requires very high thermal
insulation to protect the body from burning when exposed
to an external heat source. These garments are very thick
and multi-layered, consisting of underwear, station uniform
and a triple layered fire-fighter jacket on the outside.
• Overall distribution of moisture in multi-layer protective
clothing can be influenced by using defined combinations
of hydrophilic and hydrophobic textile layers.