Co-injection molding process produces a plastic part with a skin and core laminated structure. The skin material is firstly injected into the mold, followed by the core material, and the machine injects skin material again to encapsulate the core. Therefore, a product can be made with desired appearance of outside skin material. With this character, co-injection molding is widely used to enable regrind and reprocessed materials as the 2nd shot core material, which brings environment benefits and cost reduction. Furthermore, the process is able to provide product strength and performance with high-impact plastics as core materials.