of the foamed thermoplastic film desired the decomposition products of the foaming agent that form the gaseous phase or gaseous cells 12 of the foamed thermoplastic film include air nitrogen carbon dioxide carbon monoxide and other hydrocarbons azodicarbonamides generate primarily nitrogen gas into the melt modified bicarbonates generate primarily carbon dioxide gas into the melt ultimately these gases expire after extrusion and are replaced by air within the film these gases have relatively low critical points as well as low solubility in the melt additives such as activators and nucleators in combination with the chemical foaming agent may be used in the present invention to ensure the complete decomposition of the chemical foaming agent and to control gaseous cell 12 size nucleation agents such as talc and other finely divided fillers may be used to assist in gaseous cell 12 formation by providing sites for the cells to form it is important to note that the foaming agent itself especially if used in particulate form may also act as a nucleating agent fig2 is a cross section of a typical extruder shown generally at 20 that can be used to manufacture the foamed thermoplastic film of this invention the functions of the extruder are three fold 1 to plasticate the thermoplastic resin to the proper viscosity so that it can absorb the gas generated by the foaming agent 2 to intimately mix all components of the resin foaming agent mixture together and 3 to maintain the resin foaming agent mixture under sufficient pressure so that the gas produced.