A car bumper is made by a process called reaction injection molding (RIM), which basically consists of making a special polyurethane compound and introducing it into a large bumper moulding. RIM is a process that conserves raw materials and reduces costs. It is similar to injection molding except thermosetting polymers are used, which requires a curing reaction to occur within the mold. Common items made via RIM include automotive bumpers, air spoilers, and fenders.
As to automobile's bumper, it is the front-most or rear-most part, ostensibly designed to allow the car to sustain an impact without damage to the vehicle's safety systems. They are not capable of reducing injury to vehicle occupants in high-speed impacts, but are increasingly being designed to mitigate injury to pedestrians struck by cars.
In the process of making car bumper, there are two steps. The first step is making a Polymer. Liquid plastic precursors are mixed with a catalyst that causes them to combine and polymerize rapidly. The materials then are poured or injected into a large mold, where they combine rapidly, according to Gusmer Decker. And the next step is using the car bumper mould. The result is a polymer of polyurethane. With the help of gas, the polyurethane expands to fill the bumper mold, according to History.com. The lightweight product then is removed.