For the clothing insulation to be ‘just right’ it will maintain body temperature and comfort by the avoidance of the need to sweat and by maintaining the mean skin temperature at around 33 degree Celsius. A strategy for selecting appropriate clothing for activity in cold environments is to calculate the clothing insulation required for the whole-body and then to provide additional clothing (mitts, gloves, hat, etc.) for the protection of the extremities. Wind chill is related to the cooling effect on a local skin segment and thermal resistance or insulation required is defined as “required clothing insulation for the preservation of body heat balance at defined levels of physiological strain”. Evaporative resistance of clothing is wettedness (dry skin) divided for normal clothing and multiplied by the total clothing resistance. Evaporative heat exchange is wettedness multiplied by the partial vapour pressure gradient between skin and air divided by the evaporative resistance of clothing.