Modular window encapsulation of glass using Polyurethane RIM (Reaction Injection Molding) has been very popular in the automotive industry over the last 10 years. RIM offers many advantages in the design of modular windows including: flexibility to design complex shapes with variable wall thicknesses, molded-in attachment studs for easy assembly, and aerodynamic styling.The automotive industry is continually looking for new advancements in technology to increase productivity and decrease the costs of processing parts. A processing advancement using IMR (Internal Mold Release) was introduced into RIM bumper fascia in 1982 with great success. To this day, IMR is an important component for automotive fascia applications. Likewise, window encapsulation with the use of IMR in RIM systems has become a key component in reducing molding cost for automotive windows.The introduction of IMR in RIM for Window Encapsulation offers many potential benefits to the molders of these parts. The advantages include increased molding efficiency for RIM window encapsulation by reducing the need for spraying external mold release and also reducing the mold cleaning time. The use of IMR in the window encapsulation industry has already enhanced the productivity of the RIM molding process.Before IMR could be used in a new RIM formulation for a production application, a major question was raised as to whether the use of IMR technology would interfere with the adhesion of the RIM material to the glass. This paper will explain the adhesion testing and data analysis techniques used for window encapsulation RIM systems and present results for RIM systems with and without IMR. Proof of strong adhesion was required before the automotive industry would accept this new component in window encapsulation formulations. Adhesion was tested after exposure to a variety of aging and environmental conditions. The results of the analysis will show that chemical bonding between the primer and the glass does not decrease with the use of IMR.