text: EPE foams were first manufactured in the 1970s.
  Production of the PE beads is usually by extrusion, followed by chopping, producing a pellet. Autoclave expansion is the most common route the bead foam. Butane or pentane is often used as a blowing agent (before 1992 CFCs may have been used). Depending on the specific process uses the beads may be cross-linked either by electron beam irradiation (see Electron beam processing), or by the addition of a chemical agent such as dicumyl peroxide.
  An alternate route (JSP Process) to the beads uses carbon dioxide as a blowing agent which is impregnated into the pellets in an autoclave at a temperature close to the plastic's crystalline melting point. The pellets are foamed by "flashing" into the (lower pressure) atmosphere to expand.
  Finally molding is done by steam chest compression molding; usually the low pressure variant of the process is used, though the high pressure variant may be used for HDPE based EPE foams.