In this context, ceramic just means non-metal and non-organic. Plenty of ceramics have decent thermal conductivity - in fact, diamonds are ceramics and they are

In this context, ceramic just means non-metal and non-organic. Plenty of ceramics have decent thermal conductivity - in fact, diamonds are ceramics and they are some of the most thermally conductive things ever. However, ceramics are very much not something you can thermoform. Even silicone (aka siloxane polymers) can’t be thermoformed. I’m not a huge ceramics expert but every ceramic I’ve ever used has been a thermoset.