Basic measurement for the thermal properties of clothing. One clo unit is the thermal insulation that is comfortable for a resting man at 21 °C, where relative humidity is less than 50% and the air movement is 6 m/min: it equates to a man wearing a three-piece suit and light underclothes. At –40 °C, 12 clo units are required; light activity lowers this to 4 clo units, and a person running at 16 km/h would be adequately protected by only 1.25 clo units of clothing. The amount of protection required increases when clothes become wet, because water is a poor insulator.
Subjects: Sports and Exercise Medicine.