Thermal conductivity heat flow may not be exactly the same as the direction of the thermal gradient. In metals, thermal conductivity approximately tracks electrical conductivity according to the Wiedemann–Franz law, as freely moving valence electrons transfer not only electric current but also heat energy. However, the general correlation between electrical and thermal conductance does not hold for other materials, due to the increased importance of phonon carriers for heat in non-metals. Highly electrically conductive silver is less thermally conductive than diamond, which is an electrical insulator, but due to its orderly array of atoms it is conductive of heat via phonons. The
Interfacial thermal resistance of the spectrum, one of the highest thermal conductances "measured" is between aluminum and copper. At room temperature, the Al-Cu interface has a conductance of 4 GW m K. The high thermal conductance of the interface should not be unexpected given the high electrical conductivity of both materials. The superior thermal conductivity of Carbon nanotubes makes it an excellent candidate for making composite materials. But interfacial resistance impacts the effective thermal conductivity. This area is not well studied and only a few studies have been done to understand the basic mechanism of this resistance. Interfacial thermal resistance Interfacial thermal resistance,