The much discussed ″wet bush″ will make its way in various types. Mixing and shearing screws help to increase the efficiency of extruders. The parameter determining the extruder performance is not the diameter, but the torque of the screw. Mechanical engineering and process engineering must be adjusted. A decisive factor is the proper controlled system, but not the question of whether cooling by air or water should be used. A necessity for computerized extension control is pointed out.