Several simulation models have been applied to the RIM process to predict fill patterns, viscosity effects and curing behavior. The following topics are discussed: 1) An improved mold gate design to reduce air inclusion is recommended based on experimental and theoretical results, 2) The effects of mold and component temperature on curing and flow are predicted and compared to experimental results for a polyurethane/urea system. Based on these results, optimal process conditions to speed cure without hindering flowability are recommended. 3) The location of flow front propagation and knit lines is predicted for flow through an obstructed plaque. This type of analysis is becoming increasingly important for the efficient design and debugging of new tools, and for optimizing production conditions as new RIM chemistries and more demanding applications are introduced in the future.