Clothing insulation

Clothing insulation is the thermal insulation provided by clothing.

Even if the main role of clothing is to protect from the cold, protective clothing also exists to protect from heat, such as for metallurgical workers or firemen. As regards thermal comfort, only the first case is considered.

There are three kinds of heat transfer: conduction (exchange of heat through contact), convection (movement of fluids), and radiation.

Air has a low thermal conductivity but is very mobile. There are thus two elements that are important in protecting from the cold:

Another important factor is humidity. Water is a good conductor of heat, thus if clothes are damp — because of sweat, rain, or immersion — water replaces some or all of the air between the fibres of the clothing, causing heat loss through conduction and/or evaporation.

Thermal insulation is thus optimal with three layers of clothing:

The three layers of air between the skin and the exterior layer also play an insulating role. If the clothing is squeezed tight (as by the straps of a backpack), insulation will be poorer in those places.

Clothing insulation may be expressed in clo units. The clo has the same dimensions as the R value used to describe insulation used in residential and commercial construction. The clo value is also similar in magnitude to the R value:

This is the amount of insulation that allows a person at rest to maintain thermal equilibrium in an environment at 21°C (70°F) in a normally ventilated room (0.1 m/s air movement). Above this temperature the person so dressed will sweat, whereas below this temperature the person will feel cold.

There are a number of ways to determine clothing insulation provided by clothes, but the most accurate according to ASHRAE Fundamentals are measurements on heated manikins and on active subjects. Equations may then be used to calculate the thermal insulation. Because clothing insulation cannot be measured for most routine engineering applications, tables of measured values for various clothing ensembles can be used. According to ASHRAE-55 2010 standard, there are three methods for estimating clothing insulation using the tables provided.

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