In 1982 the introduction of Internal Mold Release systems revolutionized the Reaction Injection Molding (RIM) polyurethane fascia industry. IMR technology significantly reduced the frequency of spraying external mold release agents, making substantial increases in productivity possible. This technological gain has been industry proven and well documented.IMR technology can benefit the molding efficiency for RIM window encapsulation by reducing the need for spraying external mold release and by reducing the mold cleaning time. The unique requirements for manufacturing modular automotive windows mandated that the standard IMR systems, used for fascia, were not suitable for this application. New IMR systems were developed which improved storage stability and flowability, while providing excellent releasability, physical properties, adhesion, and processing.This paper details the selection criteria for an IMR system for window encapsulation, as well as test results for the commercial system, MP-10,000IMR.