The foaming of thermoplastic polyurethanes with CO2 as a blowing agent reduces materials input for existing applications and in addition leads to improved materials properties for new applications. Therefore the co extruder machine correlations between procedure parameters and the resulting foam top quality will be examined in this paper. The solubility behaviour of CO2 in the polymer melt is certainly analysed by means of a high pressure sorption balance. For the foam extrusion of the shear and temperature sensitive polymer, the affect of the screw geometry on the extrusion method is examined. Initial extrusion experiments have resulted in TPU foams with a density below 0,4 g/cm3.