clo Defined

For the benefit of those who may have felt distressed upon encountering a unit of physical measurement called the “clo”, and for the edification of those for whom it is new, the Canadian National Research Council in Ottawa has issued an explanation through its public relations office. The clo, which is descriptive of the thermal efficiency of clothing, was adopted during World War II, according to the Council, as being somewhat more simple than the normal expression defining insulation in terms of “calories per second per square centimeter per degree centigrade temperature difference”, or the alternative used in engineering circles, “British Thermal Units per hour per square foot per degree Fahrenheit temperature difference”. The unit is roughly a measure of the amount of clothing insulation which the usual resting man might find most comfortable in an environment of seventy degrees Fahrenheit with a relative humidity of fifty per cent and an air movement of ten feet per minute. The clo is being put to good use, it appears, by the Council’s physics division, which is equipped to measure the thermal conductivity of textiles in still air and in winds up to twenty‐five miles per hour.

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