For years the injection of physical blowing agents during the extrusion of thermoplastic materials has been state of the art. Recently at the institute of plastics processing (IKV), Aachen, it has been investigated whether injection moulding with physical blowing agents can be adapted to the extrusion of rubber materials. Using a laboratory extruder, basic knowledge is developed concerning the production of sponge rubber profiles with nitrogen as blowing agent. In first experiments the influence of nitrogen injection on the processing behaviour and the main influences of process parameters on the profile quality have been determined. Primary objective of these investigations is the development of a stable lab-scale process for the extrusion of sponge rubber using physical blowing agents.