Thermal garments are garments to withstand the climatic condition of below 30°c. These garments provide warmth to our body and make us to feel comfort even in the sub zero temperature conditions. Apart from the normal clothing performance these garments should perform with required functional properties to meet with the climatic conditions. These garments are mainly divided into three different structures and apart from these structures additional gears are also considered along with the garments. Three different structures are inner structure, mid layered structure, protective layers. The extra gears are like helmet, gloves, shoes, socks etc.
Cold is a hazard to human health. Cold environments may affect human physiological as well as human psychology. The main aim of the thermal garments should be prevention of cooling and maintenance the heat balance at acceptable temperature level. The aim of thermal garments is to give barrier effect. The clothing should shield the body from outside condition1. Ergonomics and psychological consideration plays important role in determining the performance of thermal garments.
The comfort factor is important for all garments, while considering thermal garments comfort consists of various factors like weight of the garment, breathability, thermal insulation, permeable to moisture vapor, wind resistance etc8.
The acceptance of uncomfortable clothing by the users was sometimes very low and the purpose of that clothing may not be fulfilled. The aim of the functional clothing is to give protection from rain, snow or wind. The construction of the textile fabrics must fulfill the requirements, like the fabric should be wind proof and water repellent, water vapor transmission should be possible from the skin to outside of the clothing and winter clothing should be heat insulated2. Along with all, thermal comfort is important, which is defined as “Condition of mind towards the environment which express the satisfaction of the garment”. Thermal comfort comprises of important factors like, perception of warmth, humid, transportation of vapor, etc.
To study about the thermal resistance and evaporation one should know about the heat and mass transfer mechanism. Especially heat transfer mechanism like conduction, convection and radiation and its significance.
Heat transfer is energy in transit due to a temperature difference. Heat exchange between the body and the environment takes place at the skin surface by three ways namely, conduction, convection and radiation. Existence of a temperature difference between or in a medium leads to heat transfer. Heat and mass transfer plays important role while evaporation and body metabolism.
Apart from convection, conduction and radiation, heat loss may occur due to evaporation and respiration5. In the generated heat approximately 10% of human heat loss due to breathing, the majority is drawn off through skin. This loss of heat occurs in two ways, a dry heat transfer and moist heat flow. Dry heat transfer which is of radiation and heat conduction. Moist heat flow due to the evaporation of perspiration, we can say it as moisture transfer. Heat exchange from the skin to the environment is mainly influenced by the air temperature, humidity, wind speed, solar, sky, and ground radiation, and clothing.