Fiberglass reinforced composites have been utilized by automotive designers and engineers for over forty years. Structural RIM, or SRIM, is one of the most innovative approaches developed in recent years for volume production of these composites. Material developments at ICI have resulted in SRIM systems with outstanding processing characteristics and property performance relative to earlier materials in the field. This new generation of SRIM materials posseses excellent thermal stability, mechanical properties, and retention of properties after exposure to harsh environments typically encountered in certain applications such as under the hood components. This paper reviews a variety of thermal and mechanical properties for different glass loadings. Thermal characteristics of the neat resin are studied by dynamic mechanical analysis and thermogravimetric analysis. It is shown that the excellent thermal characteristics of the composites derive directly from the thermal stability of the neat resin. Development of a data base required to support engineering analysis and design of structural composites is also discussed. Utilization of proprietary catalyst technology allows for the design of controlled reactivity profiles, and product robustness, suitable for SRIM processing. Finally, brief attention is given to the development of systems with flame retardancy characteristics.