Good thermal but poor electrical?

[Collegeguy23]

[b]1. What are the only two materials that are good thermal conductors but poor electrical conductors? I think all metals follow the Wiedemann-Franz Law.

Diamond is, I believe, one of them.

[mgb_phys]

Sapphire isn't bad - Diamond is the best.

[Astronuc]

Alumimun nitride is an example of a ceramic with high/good thermal conductivity and relatively low electrical conductivity.
http://en.wikipedia.org/wiki/Aluminium_nitride

BN or boron nitride is another
http://www.accuratus.com/boron.html