The tandem extruder at PPI consists of a 34 mm co-rotating intermeshing twin screw extruder feeding a 40mm single screw extruder. The twin screw extruder is called the mixing extruder and the single screw extruder is called the cooling extruder. Polymer pellets or powder is meter fed into the hopper of the twin screw extruder. The polymer is plasticated in the first section of the extruder. Physical blowing agent is pumped into the next section of this twin screw, where it is mixed with the polymer. In the last section of the twin screw, the polymer-blowing agent charge is compressed to high enough pressure to dissolve the blowing agent into the polymer. The single screw extruder or the cooling extruder accepts the polymer at high pressure and cools the melt down at constant pressure. The screw of the cooling extruder is segmented and hence designed to optimize the cooling, mixing and pumping characteristics. There are three barrel sections on the cooling extruder. Heat transfer fluid is circulated through the shell side of the barrel to extract the heat out of the polymer. The die is mounted on the barrel of this cooling extruder. Polystyrene, Polyethylene, Polypropylene and various copolymers were foamed down to 3 pcf using carbon dioxide gas and to 1 pcf using VOC. Normally closed cell foams were produced in this setup.