It is a very good thermal conductor, but not the best. At low temperatures, copper is better. At very low temperatures, helium is much better.
Superfluid helium's maximum thermal conductivity is roughly 100x diamond's maximum!
They make nice (and expensive) tweeters, too.
https://www.madisoundspeakerstore.com/diamond-dome-tweeters/...
>Superfluid helium's maximum thermal conductivity is roughly 100x diamond's maximum!
Never thought about this before. Would that mean that heat propagates much more quickly? Possibly even approaching the speed of sound of the material?
Neat! At around the temperature of liquid water, it's still about five times as good as copper.