an extrusion die block providing a useful means of obtaining a polymer sheet with a highly efficient degree of gauge control comprises an extrusion passage defined by opposed surfaces and terminating in an extrusion orifice , at least one of said surfaces being provided with heating means comprising a plurality of elongated heater elements located within the die block at a distance of not more than 10 mm from the surface to be heated thereby , said elements being oriented in parallel with the major axis of each in the direction of extrusion .