thermoforming comprising providing a continuous sheet of thermoplastic polymeric foam transporting said sheet through an atmosphere of at least predominantly steam at a temperature of at least 215 u00b0 f maintaining said sheet in said atmosphere for a time sufficient to cause a decrease in the density thereof thereafter while under the influence of said temperature deforming at least a portion of said sheet to a predetermined shape and while so deformed cooling the same to cause retention of said shape and a system for carrying out said method application_number US 48942783 A description referring to the drawing the steam treatment and thermoformation apparatus 10 is designed to receive a sheet of thermoformable polymeric thermoplastic foam sheet from a suitable source such as a roll 12 the foam sheet can be of any suitable width for example from one foot to several feet or more in width such a sheet can be transported into and through a steam chamber 14 by any suitable transport means not shown for example roller conveyors or sheet edge clamp means can be used to transport the sheet through the chamber the chamber is equipped with steam inlet ports 18 which ports are in communication with a steam source 16 steam source 16 is any suitable means which can generate and transport to the steam inlet ports 18 superheated steam heated to a temperature of.