refractory; heat-resistant material
Technical term for materials that withstand high temperatures, used in furnaces, kilns, and industrial processes.
The inner wall of this furnace is made of refractory material.
耐熱 means heat-resistant in general, but 耐火物 specifically implies resistance to fire and very high temperatures.
Compound of 耐火 (fire-resistant) + 物 (thing, material).