Wood Plastic Composite (WPC) is a novel interesting material. With respect to wood it shows better durability in wet environment and can be obtained from recycled materials. With respect to plastics the main advantage is its lower cost. Nevertheless WPC shows also problems: the large viscosity due to the presence of high concentrations of filler and the degradation of cellulose during processing. The second problem can be avoided by processing the WPC at low temperature and this makes the first problem worse. Moreover, degradation is influenced also by the residence time in the extruder. These problems make WPC processability challenging in that the interplay among the various processing variables (thermo-rheological properties, geometry, power and operating conditions such as screw speed and barrel temperature) makes it difficult to find an optimized set of parameters. The aim of this work is to develop a methodology to optimize the WPC extrusion process by means of a model to achieve easier processability and to reduce degradation. The model is based on the one in [1]. The outputs are: flow rate, pressure and temperature profiles and residence time in the extruder. Temperature profile and residence time make it possible to estimate degradation, while the pressure profile can be useful for determining the extruder operating point. In order to validate the model, the experimental pressure profile has been measured, at various screw speeds, along a 50 mm single screw extruder (L/D = 40) equipped with a venting zone. A PP-based WPC compound was used with different concentrations of wood fibers (30, 50, 70% wt.). By comparing the pressure data with the calculations it was found that the latter are overestimated. This could be due to a partially filled channel in the solids conveying zone and to slip phenomena in the metering zone. [1] Z. Tadmor and C.G. Gogos, Principles of polymer processing, Wiley (1979)