The simulation program SIGMA, which can be used to assess the compounding process on tightly-intermeshing, co-rotating twin screw extruders, was developed within the framework of a joint project conducted by the Institut fur Kunststofftechnik (KTP) of the University of Paderborn and fifteen industrial companies of several fields in the polymer industry. The program presented here permits calculations based on physical mathematical models of the pressure, temperature, local degree of filling, melting, residence time, mixed substance characteristics derived therefrom power consumption, and degree of dispersion of the machine. These results assist the designing process engineer in the optimization of existing equipment or in the designing of new equipment.