Reaction injection molding and injection molding have almost the same name, so even experienced engineers and designers might think they are same process. But “Reaction” signals a big difference – unlike injection molding, RIM techniques utilize low-viscosity liquid polymers in thermoset – not thermoplastic – processes. Through a variety of chemical reactions, these polymers expand, thicken and harden only after they’re injected into the heated mold, accommodating much more intricate designs than ordinary injection molding. Raw materials and molding techniques can be selected and even customized to precisely deliver desired weight, strength, density and hardness characteristics. The result is large polyurethane parts with much lighter weight than those created by more commonplace processes.