Materials and its design:
the material used for this purpose must possess high thermal insulation characteristics, but as we have discussed our textile materials are poor in thermal resistance. But as we know well that air is a good insulator hence trapping air we can achieve the required property. Effective thermal garment can be designed on the principles of layering concept. Several layers of fabrics laid one over the other to form the structure. Protection against cold is mainly depends on its insulation behavior, which depends on the structure thickness. This structure performs best with the comfort and thermal insulation. Layered structure principle is divided into three main layers namely, inner layer, mid layer, outer layer.
The inner layer is worn next to skin, which have a contact with the body and controls the microclimate temperature and humidity. As we know the body activity generates heat energy. At low activity the heat energy is less and to avoid imbalance, convection supposed to take over there, for this the fabric layer must reduce the air movement. With high activity the generated heat energy cause raise in body temperature. The generated heat and moisture should transport out of layers to cool the skin.
Moisture control can be performed by absorption and transported to next layer or by ventilation. Presence of moisture/ water leads to lesser insulation performance, because water conducts heat much more than air. So the inner material is such that absorbs the moisture and dries the inner portion to keep it dry. Absorption reduces skin humidity and makes body more comfort. If the moisture remains in the body system cause imbalance in heat at further stage.
Microclimate temperature quickly rises with sweating, in this case if we are using hydrophobic fibers such as polyester, polypropylene as a structure material in the inner layer which is worn next to skin, gives better moisture transport to the next layers. But in the case of cold protection wetting of layers must be avoided at all time. The conditions are such that, inside sweating or outside rain or snow. Moisture and moisture accumulation control in cold environment is important.
Middle layer provides insulation. Depending on requirement it comprises thicker layer of materials. In winter the body activity is low, hence the heat should not escape from the body through the garment. So the mid structure should provide insulation by trapping the air inside its structure, as we know more air inside results better insulation. Selection of material for this reason is completely arbitrary.
Outer layer must provide protection against environment conditions like wind, rain, snow fall, abrasion, etc. This layer acts as a wind cheater incase of high wind rates. The type of material may be of coated fabric, micro porous structure where moisture vapor can pass through but wind and water droplets can not.
The level of insulation mainly depends on the percentage of air trapped inside the textile structure. Table shows us the percentage of air trapped and the fiber quantity in various textile structures. From this table we can say the Fur coat and Blanket having much more quantity of air than the fiber. And those two materials show better thermal insulation performance ion the day to day uses.
Apart from material characteristics, the design and fit of garment plays crucial role in thermal properties. Heat transfer may influence by the body movements too. The air gaps between the layers and openings results different effects on its thermal insulation. 75% of the heat losses are due to loss through the openings at the place like the neck, the waist, the wrist and the ankles.
Securing our high altitude borders and lands is important in the international arena. Each and every country spends around approximately 40% of its budget wealth to their army and military purposes. The task to provide safety and comfort to the soldiers at high altitudes and sub zero conditions is difficult and costliest. Military personals in the sub zero conditions and high altitudes faces lot of problems both in psychology and physiological way. The main problem faced by the military personals in the cold region is “cold injuries”. The major cold injuries are frostbite; trench foot, immersion foot and hypothermia. Apart from these injuries, there are three major clinical problems can occur with acute exposure to high altitude. They are Acute Mountain Sickness (AMS), High-Altitude Pulmonary Edema (HAPE), High-Altitude Cerebral Edema (HACE) 7.
Role of DMSRD:
DMSRD developed a garment for Indian military personals. This made up of acrylic pile fabrics and aluminized layer as insulating inner layer. This aluminized fabric kept closer to the body surface to avoid heat loss. The outer most layers designed as wind cheater with polyurethane coated nylon fabric.
The lower trousers were designed with the concept of multi layered and multi component materials. Structure consists of polyester batting and layer of aluminized fabric sandwiched together. The outer most layers designed with respect to Indian environment and climatic conditions. On the whole inner structure mainly designed with acrylic and polyester fabrics and outer structure designed with coated and treated nylon structure.
Treating the wool fiber with low temperature plasma results change in its mechanical properties, air permeability and thermal properties. Low temperature plasma technique is used to modify the textile surface structures. Action of the low temperature plasma is mainly active with the surface to influence its surface characteristics. Low temperature plasma increases the thickness and alters the surface morphology. Like induces certain degree of roughness. This changes in the surface structure results changes in the air permeability. Treated fabric shows higher thermal insulation than the un treated. Etching with low temperature plasma results creation of rough surface with voids and spaces. This increases the quantity of air trapped inside the structure, which facilitates higher thermal insulation12.
Designing garments for the military personals for high altitude ranges is difficult task and to execute this we need to consider various parameters like Heat transfer rate and loss of metabolism, environmental conditions, wind and snow fall rate, soldier’s physique. Apart from these choice of materials, material properties, design features etc.
Developments in the fiber science may lead us to extreme different route; incorporation of microfibers in to the inner structure may provide better insulation property due to their larger surface area. And in the mean time reduction of weight can be achieved easily. Introducing nanotechnology into the thermal clothing science may also give us favorable results.
On the whole various works shows us the successful design is multi layered structure and still used widely against to cold.