Introduction:
Will you
be working outside this winter? You probably already know that the best
protection is dressing with perfect wear. But do you know what materials work
best to keep you warm? System design of cold weather protective clothing is a
critical process, as it involves consideration of the effects of a number of
external and internal parameters like environmental factors and physical,
physico-mechanical and psychological parameters. The bulk and weight of the
textile materials used in cold protective clothing plays very important role in
deciding the performance of the garments, it should be as low as possible, so
that the clothing does not create physical stress and discomfort to humans and
does not affect their daily duties adversely. The primary function of cold
weather protective clothing is to protect the individual from the natural environment.
For civilians, the designing of protective clothing is simple, as the only
requirement is protection against cold, whereas for military personnel, hill
climbers, and other paramilitary forces, besides thermal insulation, a number
of other requirements are also important.
Requirements of cold protection:
Ease of
handling combat and operational hazards, accomplishing their mission with the
clothing on their body, protection against rain, snow ingress, and extreme
conditions of cold and wind. All the above requirements have to be met by the
protective clothing, and at the same time the wearer should not feel any
discomfort.
1.
To repel water and snow.
2.
To prevent heat from dissipating
to the environment.
3.
To give comfort to the wearer by
preventing the body heat from escaping out more rapidly than it is produced or
to enter the cold to the body because the lower the rates of heat flow, the greater
is the heat resistance of the material.
4.
Moisture repellent because the
moisture increases the rate of conduction, because water fills the fabric voids
and conducts heat more rapidly than air.
5.
Clothing must permit the moisture
vapour to flow out of the clothing to avoid condensation of sweat inside the
clothing at low temperature.
This
review discusses the essential factors involved in designing and developing of
cold weather protective clothing and different insulating materials available
for the weather protection.
Wool:
Wool
is a truly unique natural fibre with excellent warm properties. Wool is
generally obtained from animals such as sheep, cashmere from goats, mohair from
goats, etc. To protect oneself from extreme cold weather, wool is the perfect
material to keep warm compared to acrylic and cotton.
Wool has
several different qualities that distinguish it from other fibres. Some of the
characteristics are crimps, scales, elasticity and it grows in staples
(clusters). Wool's scaling and crimp make it easier to spin the fleece by
helping the individual fibres to attach to each other, so they stay together.
Because of crimp, wool fabrics have greater bulk than other textiles and they
hold air which causes the fabric to retain heat. Also when oiled and tightly woven,
it is waterproof to some extent. Wool makes a great choice for clothing that
can insulate you from both cold and heat. And an added bonus is that, it is
fire-resistant. One of the great properties of wool is that it readily absorbs
water due to its structure and chemical composition. Water binds within wool's
structure through the action of hydrogen bonds. The water enters the amorphous
region of the intercellular cement and the matrix of the fibre within the fibre
cortex, where the pore diameter is as small as 4nm. The moisture absorption and
desorption characteristics of wool provide important functional characteristics
to wool garments. As a result, wool acts as a buffer, absorbing the extra
moisture quickly and dissipating it gradually. All fibres do this, but wool's
performance is superior and faster. So in typical winter conditions, it can
provide real benefits to the wearer. Because of their crimped nature, when wool
fibres are packed together, they form millions of tiny air pockets which trap
air, and in turn serve to keep warmth during winter. When moisture is absorbed,
tiny amounts of heat is generated. This warmth acts to prevent condensation in
construction cavities by maintaining the temperature above the dew-point in
damp conditions. While absorbing moisture wool releases energy in the form of
heat, thus raising the temperature of its surrounding areas. Even when wet,
wool has great wicking abilities and lasts forever. Actually wool absorbs water
from both your skin and the atmosphere around you to create dry and warm
environment around your body. So to protect yourself from extreme cold weather,
as compared to the other fibres wool is the perfect material to keep you warm.
Hence woollen wear is a necessity for winter, especially in temperatures of 0
degrees and below. Merino wool is one of the most fine and versatile amongst
the natural fibres for its ability to keep the wearer warm in cold temperatures
and cool and fresh in the hottest climates. For winter apparel major uses of
wool are sweaters, hats, gloves, coats, scarves, blankets, drapes, etc.
Thinsulate:
Thinsulate
is one of the synthetic fibres for thermal insulation used in clothing.
Generally it is thinner than the polyester fibres. Thinsulate is more effective
due to increased density of fibres and decreased size of fibres. Like most
insulating materials, the gaps between fibres not only reduce heat flow, but
also allow moisture to escape. These insulating fibres are beneficial for
retaining some of the heat produced by body like sweat and other energy.
Another great property of thinsulate is its thin-ness. It is considered as 'the
warmest thin apparel insulation available'. The major drawbacks of this fibre
are its durability and it resists becoming wet. Unfortunately, it lasts less
than five years. Hence its production is carried out on small scale.
Down Feather:
"Down" refers to the undercoating
of waterfowl, including goose, duck, or swan, consisting of light fluffy
filaments (barbs) growing from a quill point but without a quill shaft".
The goose or duck down, it is still the best overall insulator. It is generally
from plumage which means outer coating of the birds. Their length varies from
10mm to 60mm. Down feather will become thick and dense in winter to protect the
body from severe cold. It absorbs water and emits its faster. It is
lightweight, compressible and will last a lifetime. However, it is expensive
and useless when wet. Also it provides no insulation and takes a long time to
dry. It is not recommended for sweat producing activities.
Special uses:
Deep sea diving:
The deep
sea suit should consist of a one-piece waterproof material that entirely covers
the wearer except the hands and head. The main job of the suit is to protect
the wearer from Hypothermia from immersion in cold water. Hypothermia is a
condition in which core temperature drops below the required temperature for
normal metabolism and body functions, which is defined at 35 degree Celsius.
Depending on the variability, the end result is usually death. So in deep sea
and oceans, the core temperature of the body falls gradually, as it is cold
below. Some of the examples of fabrics used for deep sea suits are Gore-Tex and
Nomex. They are waterproof, breathable fabric membrane generally made up of
rubber or canvas. These materials have 24 different layers to protect the
wearer from different temperatures and conditions. They are able to repel
liquid water while allowing water vapour to pass through. It is designed to be
light in weight for creating ease in swimming under waters.
Military Personnel:
Staying
warm and dry is critical for mission success. Some fibres or filaments help you
do that, by constructing lightweight fabrics and then incorporating our
technologies to enhance performance. Generally high level of protection is
necessary in cold weather and regions without exerting considerable physical
stress on the wearer. Hence designing of such fabrics is very critical, as it
involves selection of appropriate textile materials and strategy for their use.
Wool and woollen pile fabric have been the oldest materials used for providing
warmth. After the invention of synthetic fibres, utilisation of acrylic fibres
and polyester fibres in different forms is exploited for the same use.
Systematic studies on wool, acrylic pile, and polyester batting revealed that
polyester batting has good insulation/weight ratio against extreme cold. This
makes polyester batting one of the important constituents in protective
garments, where weight of the garment is of prime concern, especially in
glaciers and snowy regions. The focus is on minimizing the heat loss from the
body to the environment, so that the metabolic heat generated from the body is
not lost to the environment and instead keeps the body warm. Simultaneously the
material should allow evaporation of sweat to the environment. In extreme cold
conditions, the sweat gets frozen and causes frostbite.
Hill Climbers:
With
winter conditions firmly established on the hills, there is a need of
comprehensive look at the technicalities of textiles for staying warm. Our
human body is homoeothermic (warm-blooded) and its core temperature must be
maintained. Hence to survive cold conditions, reducing one's heat loss or
enhancing one's heat production is essential which can be achieved through the
use of perfect warm clothing. The efficiency of the climber in mountainous
region is affected to a considerable extent by the clothing worn. The clothing
must be compatible during climbing operations as well as prolonged periods of
inactivity. The main role of insulating clothing is to conserve the body's heat,
which serves as the heat source in clothing system. So use of thicker material
is advantageous which will trap a thick layer of air making it warmer to wear.
Generally, wool fabric is chosen or another way is to dress in layers. Many
insulating materials are available in the market and one has to keep in mind
all functional requirements of the protective clothing before selecting a
suitable material for designing the clothing.
Reference:
1.
Nishkamkasturiya,
M.S.Subbulakshmi, S.C.Gupta and Hans Raj. System design of cold weather
protective clothing. Kanpur - 208 013.
2.
Mathur, G.N,; Hans Raj
&Kasturiya, Nishkam. Protective clothing for extreme cold region. Indian J,
Fibre Textile.
3.
Walker, Joan M. A systematic
analysis of alternative concept for aircrew cold weather clothing. 1983. 35p,
Report No. Natick/Tr - 84/045.
4.
Gagge, A.P, Burton, A.C. & Bazett,
H.C. A practical system of units for the description of heat exchange of man
with his thermal environment. Science, 1941, 428-30.
5.
Farnsworth, B. & Nordli, B.
Measurement of the combined heat and water vapour flow through clothing under
transient conditions. Defence Research Establishment, Ottawa, Canada. Report No
DRE-82-13.
6.
Burton, A.C. & Edholm, O.G.
Man in a cold environment. Edward Arnold Ltd., London, 1955.
7.
Spearman, Richard Ian Campbell
(1973). A Textbook of Skin Biology.
8.
Peggy Bolz. The right stuff for cold weather. www.lhsfna.org
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