Abstract: Acoustical insulation or sound absorbing material particularly useful as automobile muffler material, having high temperature, vibration and chemical resistance, and of sufficient structural rigidity to resist packing or degradation when exposed to engine heat, vibration and exhaust gas pressures, formed of an alumina-silica ceramic fiber matt or blanket impregnated with a colloidal silica binder. The muffler acoustical and thermal insulation can be in the form of a hollow cylindrical body of alumina-silica fibers coated on its inside and outside surfaces and on its ends, with an aqueous colloidal silica sol, and the material dried.