Unlike most electrical insulators, diamond is a good conductor of heat because of the strong covalent bonding and low phonon scattering. Thermal conductivity of natural diamond was measured to be about 2200 W/(m·K), which is five times more than copper.

Mono-crystalline synthetic diamond enriched to 99.9% the isotope 12C has the highest thermal conductivity of any known solid at room temperature: 3320 W/(m·K) (7 -8 times copper {401 W/(m·K). Because diamond has such high thermal conductance it is already used in semiconductor manufacture to prevent silicon and other semiconducting materials from overheating. At lower temperatures conductivity becomes even better, and reaches 41000 W/(m·K) at 104 K (12C-enriched diamond).