Abstract: Composition of matter adapted to be foamed into essentially a closed cell structure, preponderance of the cells being less than 500 microns in size and containing a chlorofluoroalkane of 1 to 2 carbon atoms, said composition comprising chlorinated polyvinyl chloride resin, and effective amount of a blowing agent, an effective amount of a nucleating agent, and 5 to 20 parts of a processing aid per 100 parts of said resin, said processing aid has a dilute solution viscosity of greater than 2.5 and is selected from copolymers of styrene and acrylonitrile containing 10 to 40% of acrylonitrile.

Abstract: Composition of matter that can be foamed to form an expanded product having density of less than 20 lbs/ft.sup.3 and containing a preponderance of the cells in the size range of less than 500 microns comprising a mixture of chlorinated polyvinyl chloride, 5 to 50 parts by weight of the chlorofluoroalkane of 1 to 2 carbon atoms as a primary blowing agent and 0.01 to 2 parts by weight of azodicarbonamide that is dispersed through the resin and forms cell nuclei from which expanded cells are created, all based on 100 parts by weight of the resin.