Up until now, however, nobody could really explain how these convection currents emerge in the first place: iron is a very good heat conductor and at high pressure its thermal conductivity increases even more. (sciencedaily.com)
Plus: aluminum is lightweight and a great heat conductor, too! (geekwrapped.com)
Nanotubes are also excellent heat conductors and in some configurations are semiconductors. (sciencemag.org)