With the increasing demand for plastics as replacements for such conventional materials as glass, metal, and wood in a wide variety of applications, there have been more and more industrial processes in which polymer melts are extruded through dies of complex cross section to form the final product. The shape of these dies and the pressure losses through them are important factors in pre- venting flow defects and controlling the quality of the end product. Predic- tions of pressure losses through dies of complex cross section have not been as popular a subject in the literature as flow through circular cross-sectional dies.