1. (thermal conductivity) A measure of the ability of a substance to conduct heat. For a block of material of cross section A, the energy transferred per unit time E/t, between faces a distance, l, apart is given by E/t=λ‎A(T₂ − T₁)/l, where λ‎ is the conductivity and T₂ and T₁ are the temperatures of the faces. This equation assumes that the opposite faces are parallel and that there is no heat loss through the sides of the block. The SI unit is therefore J s⁻¹ m⁻¹ K⁻¹.

2. (electrical conductivity) The reciprocal of the resistivity of a material. It is measured in siemens per metre in SI units. When a fluid is involved the electrolytic conductivity is given by the ratio of the current density to the electric field strength.

http://www.kayelaby.npl.co.uk/general_physics/2_3/2_3_7.html Values of thermal conductivity for a range of materials at the NPL