this invention provides packages and containers produced by a solid state method for the manufacture of foamed polymeric material . the packages are suitable for pre - cooking or sterilization , insulated transport , cooking vessel , reheating , and storage of food . the gas impregnated thermoforming process includes interleaving an article of raw polymeric material with a gas channeling means ; exposing the article to a non - reacting gas at elevated pressure to achieve a desired concentration of gas within the polymer , thereby forming a partially gas - saturated article , separating it from the gas channeling means , then decompressing , foaming and forming it at a temperature below the material &# 39 ; s melt temperature ; and finally trimming it to produce a finished foamed polymeric material and recyclable scrap solid state process foamed polymer .