The modeling of the laminar, isothermal flow of a thermosetting polymer through a coat-hanger die was investigated. A complete model of the flow through the rectangular channel alone was not satisfactory for large times, unless used with a grid moving with the growing layer of gelled polymer formed near the walls. In addition, an approximate analytical solution assuming that the viscosity-residence time curve is a step function gave good results for large times compared to the average residence time. In view of this a simplified model, based on similar assumptions, was developed for predicting rate of buildup and pressure increase for the flow through the entire die (manifold plus slit). Its predictions are in good agreement with experimental results obtained with a polyurethane system.