CLO Value is the amount of insulation that allows a person to maintain thermal equilibrium whilst resting in an environment at 21 degrees Celsius or 70 degrees Fahrenheit. A value of 1 CLO is based on a typical business suit, which includes a shirt, undershirt, trousers, and suit jacket. The higher the CLO value, the more insulating value is provided by the clothing in question.

Clo values are generally used in relation to clothing, a method of measuring the warmth value of an article of clothing. By establishing the Clo value of an insulation, depending on the weight, loft and breathability. The most appropriate product can then be recommended for apparels expectations. For example the insulation in a running jacket would need to have a lower Clo value of around 1 due to the typical environment and activity the end user will use the jacket in, this way it is easier for the end user to maintain a more constant boy temperature with out getting to hot or to cold.  

Below is a graph showing what Clo value is recommened for clothing, in different temperatures and at different levels of activity. e.g. If someone was to be resting in a temperature of around -30°c they would need to wear garments around 8 CLO.