Over-Molding and Insert Molding

Over-molding allows plastic to be molded to a substrate. This substrate can be almost any type of material from cloth, metal, wood, or other plastics. For instance, a fastening buckle can be molded onto a nylon strap without the need for sewing or other secondary operations. 

Insert-Molding allows certain structural or aesthetic aspects of a plastic part to be inserted into the mold and the plastic will mold around the inserted part. Example, a certain part has two halves and needs to be assembled. The bottom half would have threaded metal posts molded into the part, the top half could now be affixed using simple screws, rather than other more costly ways of assembling the part.