AbstractViscoelasticity, nonisothermality, and fountain flow influence the microstructure development during injection mold filling of polymer melts and, therefore, the ultimate properties of a molded article. A comprehensive two‐dimensional mathematical model is developed to evaluate the effects of these factors on the structure of the flow field. Special consideration is given to the shape of the flow front, which is crucial in determining the structure of flow in the fountain region. The effects of slip and crystallization are also considered and their influence on model predictions are analyzed. Simulations using the no‐slip and slip boundary conditions show that a slip boundary condition is necessary to alleviate the singularities in the flow structure. The results also indicate that the predicted stress profiles are significantly influenced by the viscoelasticity of the polymer melt. Furthermore, the nonisothermality and subsequent deposition of a solid layer next to the mold walls considerably alter the moldability parameters and the flow fi