refractory

(Of a material) able to resist high temperature, for example ceramics made from clay, minerals, or other earthy materials. Furnaces are lined with refractory materials such as silica and dolomite.

Alumina (aluminium oxide) is an excellent refractory, often used for the bodies of spark plugs. Titanium and tungsten are often called refractory metals because they are temperature resistant. Cermets are refractory materials made up of ceramics and metals.