Experiments on a blow-molding grade of polypropylene have been performed at 135 degrees C using a biaxial testing machine. Both simultaneous and sequential equibiaxial tests were performed at strain rates relevant to solid phase processing regimes. A constitutive model has been developed that includes a single Eyring process and two Edwards-Vilgis networks. The effectiveness of this model for predicting the observed stress-strain behavior is explored. Predictions of simultaneous stretching and the first stretch in sequential experiments are excellent. The second stretch in sequential experiments is less well predicted, but the model's performance is useful overall. The model is incorporated into a commercial finite element code and its practicality is demonstrated. POLYM. ENG. SCI., 49:1902-1908, 2009. (C) 2009 Society of Plastics Engineers