thermal conductivity

Ability of a substance to conduct heat. Good thermal conductors, like good electrical conductors, are generally materials with many free electrons, such as metals. A poor conductor, called an insulator, has low conductivity.

Thermal conductivity is expressed in units of joules per second per metre per kelvin (J s⁻¹ m⁻¹ K⁻¹). For a block of material of cross-sectional area a and length l, with temperatures T₁ and T₂ at its end faces, the thermal conductivity λ equals Hl/at(T ₂ − T₁), where H is the amount of heat transferred in time t.