The processing properties of a rigid PVC compound with various amounts of different lubricants were studied with a torque rheometer. The plasticizing behavior was measured in a mixer and recorded as torque versus time. The fusion time and the torque at fusion and of the molten material were evaluated. The compounds were extruded with a laboratory extruder and a capillary die. The torque of the screw, the melt pressure, and temperature in the barrel and the die and the output were measured. The shear stress and shear rate were calculated from these results. The lubricants, one paraffin and five polyethylenes, had molecular weights of 700 to 3500. The dependence of the processing behavior on the molecular weight of the lubricants is discussed. There is no single value which can be given but numerous interdependent parameters can be used to obtain a prediction of the processing properties of the material.