In injection molding, plastic granules are heated and "injected" under pressure into metal molds, where the molten plastic hardens into a designated shape. The mold then opens and the newly formed part is removed and inspected, ready for shipment or secondary manufacturing operations. Injection molding is an extremely versatile and popular form of molding.

This may have the same name as the forming process for thermoplastic materials, but it does have some significant differences. With conventional thermoplastic molding, the injection unit heats up to 300-700 F depending on the material you mold. With thermoset materials, typically hot water is used and rarely does the injection unit heat up passed 200 F. Conversely, the mold temperature is usually chilled or heated only with water for molding with thermoplastics. Like compression and transfer molding, the mold must be heated to 300-400 F in order for the thermoset materials to crosslink properly. Parts made with injection molding will be typically ready to use without any secondary deflashing operations. Care must be taken to make sure the material is not overheated in the injection unit since premature crosslinking will cause the entire injection unit to feeze together.