Epoxy — Some epoxies can tolerate somewhat high-temperature (around 200⁰C / 390⁰F [1][2]). With the addition of epoxy fillers, they can be molded almost like putty.
Ceramics — Can withstand very high temperatures, but require firing in a kiln. Depending where you're at, there may be some local clay/pottery classes in a studio that can provide a little time in their kiln.
To distinguish between the artistic ceramics that many others do, the kind I'm interested in are known as "technical ceramics" or "engineering ceramics".
Metals are high-heat, but the lower-melting-point ones are easier to work with in a residential setting: