A measure of how rapidly a material exchanges heat with another body in transient contact. Here k is thermal conductivity, is mass density and is specific heat capacity. Perceived coldness at equal actual temperature can depend on this contact heat transfer rather than on an electronic Fermi temperature.
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Thermal effusivity is a property of materials that describes their ability to conduct and store thermal energy. It is a measure of how well a material can exchange heat with its surroundings or with another material when they come into contact.