A simple model based on the lubrication approximation has been developed to analyze heat transfer of power-law fluids inside an extrusion die. This model can effectively predict the influence of temperature variations and other production alterations on flow uniformity. The predictions of this model are compared with those based on three-dimensional finite element simulation, and the agreement is satisfactory. The optimal design concept can be incorporated into this model so that a specially designed choker bar can be inserted into the extrusion die to reduce now nonuniformities. The shape of the choker bar is initially suggested by the lubrication model; minor corrections through the three-dimensional finite element simulation are then introduced so that a choker bar can be properly constructed to eliminate now nonuniformities.