Primarily, RIM utilizes polyol and isocyanate mixture, known as Polyurethane. The excellent flexibility, impact resistance, and durability make it widely popular.  Additionally, it can be formulated to be rigid or flexible. Other materials and their respective properties include;

Epoxy Resins: Mechanical strength, excellent adhesion, and chemical resistance.

Silicone Materials: Biocompatibility, heat resistance, and flexibility.

Polyurea:  Fast curing times with high resistance to abrasion and chemicals.

Nylon:  High tensile strength, excellent wear resistance, and good chemical stability.

Composites: Reinforcing materials such as glass or carbon fibers for strength and stiffness.