thermal conductivity

from The American Heritage® Dictionary of the English Language, 5th Edition.

• noun A measure of the ability of a material to allow the flow of heat from its warmer surface through the material to its colder surface, determined as the heat energy transferred per unit of time and per unit of surface area divided by the temperature gradient, which is the temperature difference divided by the distance between the two surfaces (the thickness of the material), expressed in watts per kelvin per meter.