The injection mold machine was relatively simple compared to machines in use today: it worked like a large hypodermic needle, using a plunger to inject plastic through a heated cylinder into a mold. The industry progressed slowly over the years, producing products such as collar stays, buttons, and hair combs.

The injection mold remains cold so the plastic solidifies almost as soon as the mold is filled. Two-shot or multi-shot molds are designed to "overmold" within a single molding cycle and must be processed on specialized injection molding machines with two or more injection units.

This process is actually an injection molding process performed twice. In the first step, the base color material is molded into a basic shape, which contains spaces for the second shot. Then the second material, a different color, is injection-molded into those spaces.