The transitions and reactions involved in the thermal treatment of polyethylene (PE) and EVA at a heating rate of 10 degreesC min(-1) in an inert atmosphere (N-2), have been studied by differential scanning calorimetry (DSC). A brief discussion on the methodology related to the mathematical treatment of the DSC data is presented. The physical meaning of the kinetic parameters and the objectives of the DSC data reduction procedures are also commented on, emphasising the necessity of complex models in order to explain complex behaviours in detail. Different kinetic models have been suggested and applied involving one or two fractions susceptible of undergoing transitions or reactions. In addition, the variation of the heat capacities of the different fractions has been considered yielding a remarkable improvement in the fitting of the whole of DSC curves. The models applied are capable of representing the different processes observed and can be of great interest in the understanding of such phenomena, as well as in modelling the heat involved in the processing of these type of products. (C) 2001 Elsevier Science Ltd. All rights reserved.