The best conductor of heat is diamond with a thermal conductivity of more than 2,000 watts per meter per degree Kelvin at room temperature. Silver is the material with the second-highest thermal conductivity at 429 watts per meter per degree Kelvin. This makes silver the metal with the highest conductivity.
Diamond is a form or allotrope of carbon. It is extremely hard, has a high melting point and is lustrous. Although it is a good heat conductor, it is not a conductor of electricity.
Presently, diamond is the best-known thermal conductor of heat. However, research into new materials indicates that the chemical compound boron arsenide may have a higher thermal conductivity than diamond.