shape the particles being in a size range from about 40 to about 400 microns and including from about 5 to about 100 percent by weight of microporous particles of a synthetic thermoplastic polymeric material and from about 0 to about 95 percent by weight of nonporous synthetic thermoplastic polymeric material and subjecting the particles to an effective pressure from about 200 to about 8000 pounds per square inch while retaining the particles in the desired shape for a sufficient length of time to produce an integral porous structure having substantial physical integrity application_number US 55144683 A description as indicated the present method provides a facile means for producing three dimensional porous structures by use of the present invention it is possible to produce porous structures with a density less than the theoretical density of an identical structure made solely from nonporous particles of the same material at the same pressure the starting materials are particles of a synthetic polymeric material the material may be a homopolymer a copolymer or a blend of various homopolymers and or copolymers the process of the present invention applies to olefinic polymers condensation polymers and oxidation polymers typically the synthetic polymeric material will be a homopolymer of polypropylene or polyethylene exemplary.