Thermal conductivity at 25° C

Form of Carbon	Thermal Conductivity (Watts/centimeter * ° K)
Graphite	19.6 parallel to sheets 0.0573 perpendicular to sheets
Diamond	23.2
Amorphous	0.0159
C60

Thermal energy within a crystalline solid are conducted by electrons and/or discrete vibrational energy packets (phonons). A material's ability to conduct heat is known as its thermal conductivity.

The reason why one substance feels "cooler" than others at the same temperature is because of the difference of their thermal conductivity. The thermal conductivity of a substance gives a rough indication for how rigidly components within a crystalline solid are held together and how much imperfections are incorporated within a crystal. Moving components within a substance tend to scatter the heat carrying electrons and phonons, in effect reduce the thermal conductivity of that material. A prime example is that shown by graphite.

Different directions in a crystal can conduct heat at different rates. Graphite exhibits this behavior. It is highly conducting along its layers and not so well perpendicular to the layers because their is no bonding between the layers.

Do you know that you can distinguish between a real diamond and cubic zirconia by their thermal conductivity. The diamond has a higher thermal conductivity than the latter, so feels cooler to your lip.

Thermal Conduction: The transfer of heat through a substance without bulk movement of the substance; thermal conductivity symbol k, units W/(m.K) (watts per metre.kelvin). Heat transfer through poor conductors is via the thermal vibrations of atoms. Metals are good conductors, and transfer heat via conduction electrons in the free electron gas. They typically conduct heat a thousand times better than non-metals such as glass of wood.