This invention is directed to a process for forming stable, low density, fine celled extruded foam from normally crystalline vinylidene chloride polymers such process comprising (1) forming an admixture of a normally crystalline vinylidene chloride polymer in powder form with a blowing agent composed of a compound or mixture of compounds having a boiling point of less than about 40.degree.C, a vapor pressure at the foaming temperature used of greater than atmospheric pressure and less than about 1000 p.s.i. and a solubility parameter of greater than about 6.6 and less than about 8.7, then (2) extrusion foaming the admixture using an extrusion temperature of from about 120.degree.C to about 150.degree.C.