Abstract: The invention concerns a material having good resistance to mechanical stresses and heat and in particular having substantial resistance to the penetration of a directed flame such as the pointed flame of a blowpipe.The material comprises a substance which can be polymerized such as a polyurethane, sulfur, and possibly halogenated compounds, phosphorus-bearing compounds, phosphohalogenated compounds, trivalent antimony oxide, solid or liquid fillers and pigments.The material may be used for the production of strong walls, in particular by filling internal cavities of armoured doors, walls of strong rooms or safes.