non - oxide refractory foams , possessing controlled permeability and uniformity , are prepared by impregnating an organic polymer foam material with a fluid , particulate slurry of a first refractory material , drying , applying to the dried , impregnated material a second refractory material which has a lower melting point than the first refractory material and thereafter heating , at a temperature sufficient to cause melt infiltration of the second refractory material into the impregnated material , thus producing inert and dimensionally stable composite refractory foams having broad utility as particulate filters or carriers .