Prior to carbon nanotubes, diamond was the best thermal conductor known. For heat flowing along their axes, carbon nanotubes have now been shown to have a thermal conductivity of about 3000 Watts per meter-degree Kelvin [Dresselhaus et al., Phil. Trans. R. Soc. Lond. A 362, 2065 (2002)].In comparison, the thermal conductivity of diamond is between about 900 and 2300 W/m-K, while copper is only about 400 W/m-K.
The carbon nanotube’s thermal conductivity is very large along its axis because vibrations of the carbon atoms propagate easily down the tube. In the direction transverse to its axis, however, the nanotube is much less rigid and the thermal conductivity in that direction is about a factor of 100 smaller. Research at major semiconductor manufacturers is now seeking to use nanotubes to carry heat away from electronic circuitry, enabling the next generation of ultra small circuits.