What part of an ememy being made of steel make them immune to heat (found, is hardcoded)

If an enemy has it’s material listed as steel it is immune to all heat damage. I want to know if it is something in the materials.json entry or if it is a hardcoded thing.

A monster has only one material and there’s no different material for different parts.

the rust zombies have their material listed as [flesh, steel]

I didn’t know that.

I guess, a monster is fire-proof when all of its material is fire-proof.

Just looked in monster.cpp in the source code on github and yep.

if( dt == damage_heat && ( made_of( material_steel ) || made_of( material_stone ) ) ) {
return true;

steel heat immunity is hardcoded. Well guess ill just change all the materials to one of the variety of steels then.