One of the most widespread practical methods of polymer processing is the extrusion method that is based on pressing a polymeric melt through channels of the molding tool which have different geometrical cross-sections. The basic performance of extrusion is based on the pressure and flow performance which sets functional correlation between volumetric flow rate of a polymer medium, pressed through a molding tool, and created pressure drop. Arguments of this correlation are the rheological parameters of polymer and the geometrical characteristics of the channel in which the polymeric melt flows. In this article, a viscoelastic model with a corrected strain energy function is implemented. The comparison of revealed theoretical expression in this article with the experimental data for flow of polymeric melts in cylindrical channels with various cross-sections demonstrates a good convergence over a wide range of pressure gradient. POLYM. ENG. SCI., 49:478-482, 2009. (c) 2009 Society of Plastics Engineers