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 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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