Unlike vacuum casting, the Reaction Injection Molding (RIM) process does not rely on expensive vacuum chambers and mixing units.

The process uses a simple resin injection system with two pressurized chambers. Using an injection nozzle, a silicone tool is filled at atmospheric pressure until excess resin is driven up through a series of riser holes. The cure reaction time is much shorter than in vacuum casting. There is no thermal cycling and the contact time between the resin and silicone rubber is much shorter; therefore, the tools can last for up to 100 shots.