The results given in this paper are expressed in terms of watts, °C and metres. So that practical clothing may be described conveniently by a range of small integers, the unit of thermal resistance, to be called the “tog,” is the resistance that will maintain a temperature difference of 0-1°C. with a flux of 1 watt per square metre, or in more practical terms, 10°C. with a flux of 1 watt per square decimetre.