I know it depends a lot on the composition, so not all are great electric insulators. So what makes it good or bad? And is it different from what makes them good thermal insulators?
Power line insulators are ceramic and they have to stave off huge voltages. That's what got me wondering.
Best Answer
For electricity to flow, electrons need to be moving. So in a conductor, there need to be free or loose electrons so they can carry the flow of electricity. Most metals fulfill this requirement, which is why most metals are conductors. Insulators, therefore, must have their electrons bound tightly, so they cannot carry the flow of electricity. The type of ceramic used as an insulator doesn't have any loose electrons (it is not, however, a perfect insulator) so it is a good insulator. In fact, this is what makes ceramic a good thermal insulator as well: it doesn't have loose electrons!