The properties of polymer blends are conditioned to a large extent by the morphological structure of the polymer combinations employed. Since the development of the morphology inside the extruder is essentially influenced by the melting section, it is necessary to be able to estimate the melting process of binary material combinations. Part I of this publication summarises the knowledge that has been acquired in theoretical and experimental studies of melting in co-rotating, tightly-intermeshing twin screw extruders. The experimental studies reveal quite dissimilar melting mechanisms for different materials in some cases. Different models are thus available for calculating the melting process of single-component materials which have been developed on the basis of the findings established in experimental investigations. Only one model is so far familiar for the melting process of multi-material systems. This uses material values for polymer blends that have been averaged out with mixing rules to provide the basis for a calculation to estimate the melting process. Part II of the publication describes a model for calculating the melting of binary, incompatible polymer combinations which has been implemented in the SIGMA simulation software for the design of co-rotating twin screw extruders. This model can be used to calculate the temperature development in the solids conveying section and the subsequent melting process. Part III of the publication explains one possible means of investigating the melting of binary polymer combinations and discusses the results of experimental studies of polypropylene/polyamide blends. For purposes of verifying the model set out in this part of the publication, the simulation calculations are compared with the results of the experimental studies.