Synonym for a material that is resistant to fire [closed]

What is the technical term for a material that is highly resistant or insulated to fire? Such as Diamond, or Ceramics? I looked at various words already, such as Endothermic, but I'm fairly certain that is not related to the act of resisting, as it appears to be directed more towards the act of absorbing heat from the environment, such as a snowman melting. So what is the correct technical or pretentious-sounding term for a material which cannot be easily burned. I am looking for something a little bit more extravagant than "Fire-Retardant".

Usage Example:

"The snowman had been made with a new substance that made it highly resistant to both the sun, and fire, and so it was now ______, and would not melt."

"Diamond is _____, and so it is highly resistant to fire and heat."

Solution 1:

The technical term in science and engineering is refractory: having a high melting temperature or otherwise being resistant to thermal degradation. Ceramics are almost defined by their refractory nature.

Solution 2:

A common term is "fireproof". (ref.)

adjective
1 resistant to destruction by fire.
2 totally or almost totally unburnable.

Solution 3:

A friend of mine found an interesting one.

Salamandrine(adj) of, pertaining to, or resembling, a salamander; enduring fire.