This is a technical term used in the building industry to refer to products that are not capable of combustion. The glass fibers in fiber glass insulation and the rock and slag wool in mineral wool insulation have a natural fire resistance and are considered non-combustible when tested in accordance to ASTM E136.

Materials, no part of which will ignite and bum when subjected to fire.

A material which will not ignite, burn, support combustion or release flammable vapours when subjected to heat or fire