Clothes we wear have substantial effect on our ability to withstand hot an cold environmental condition by affecting the rate of heat exchange between the body and the environment. Clothing enables us protection from heat and cold by their insulation effect. It is quite clear that in very cold environment, clothing with high insulation properties help to keep the body warm by reducing the loss of body heat to the environment.
But in hot environment the relationship is not that straightforward. In warm weather the insulation of clothing increases discomfort by interfering with dissipation of body heat to atmosphere to keep the body cool. However in very hot conditions, protective clothing helps to protect the body from the adverse effect of outside higher temperature and from the effect of heating through radiation.
The amount of insulation is dependent largely on the thickness of the clothing and the amount ot of air trapped between within the fibres of the clothing.
The insulating properties of clothing is measured in units of clo. A unit clo is defined as the thermal insulation necessary to maintain in comfort, a sitting, resting subject in a normally ventilated room at 21 degrees centigrade and 50 percent relative humidity. Typically, 1 clo unit of clothing has approximately the amount of insulation to compensate for a drop in temperature of 9 degrees centigrade.
Heat transfer rate of clothing is also affected by its permeability to moisture. Permeability affects the the evaporative heat transfer through the clothing. In hot environment low permeability interferes with cooling by evaporation. In cold weather low permeability can result in wetting of clothes by sweat and thereby reducing its insulation capabilities.
While deciding on nature of clothing as protection from heat and cold, attention should be given to adequate protection to all parts of the body, including feet. Attention also needs to be paid to the impact of clothing on freedom and accuracy of movement necessary for work. For example, footwear must receive as much attention as any other apparel. Special clothing design should be considered to ensure required free movement and dexterity. For example, it may be necessary to use partial gloves in situation where finger dexterity is important.