Plastic processing generally includes mixing, shaping, machining, joining, finishing, and assembly. The last four processes are carried out after the plastic has been shaped into finished products or semi-finished products, and are also known as secondary plastic processing.

Materials used in plastic processing, in addition to polymers, generally require the addition of various plastic additives (such as stabilizers, plasticizers, colorants, lubricants, reinforcing agents, and fillers) to improve the molding process and the product's performance or reduce production costs. The additives and polymers are mixed and uniformly dispersed into powder, also known as dry blended material. Sometimes, the powder needs to be processed into granules through plasticizing. This powder and granules are collectively referred to as compounded materials or molding compounds.