A novel class of transparent polymeric foams from high T.sub.g polymers
comprising submicron cells and a process for their production is
described. The polymers are preferably high glass transition materials and
the process comprises saturating a consolidated polymer shape with an
inert gas at a temperature above the glass transition temperature of the
polymer and under a pressure of at least 9000 psi for a period adequate to
dissolve the gas in the polymer shape and then controllably cooling the
polymer shape to produce the submicron cell structure.