Injection blow molding uses the injection molding to form hollow plastic parts. Injection blow molding consist of three stations: (1) injecting plastics into a mold to form a plastic tube; (2) blowing the tube into a cavity mold to form a hollow part; and (3) ejecting the part. At the first station a split half mold closes on a steel rod called a mandrel. The mandrel forms the center of the tube. The mandrel is held in the mold much like a stick in an ice-cream bar. The mold forms the outside of the tube. The injection molder forces plastic into the mold and around the mandrel. Once the plastic tube is formed it is called a parison. The first stage is completed is when the mold opens and the mandrel is transferred to the second station. At the second station a second mold closes on the mandrel and parison. This cavity of the second mold is the shape of the final product. The mandrel, encased in the soft plastic parison, is held at the center of the closed mold. Air is injected through the mandrel, forming a hollow plastic part by blowing the soft plastic parison to the shape of the mold. After the hollow part has cooled, the mold opens and rotates to the third station. At the third station the finished part is finally ejected off the mandrel by a stripper bar.

There are several advantages in using injection blow molding rather than extrusion blow mold. In injection blow molding the part is formed in an enclosed mold, there is no scrap to be trimmed from the container. The three stations of the process allow for the formation of a thick treaded neck with a thin container wall. This features allowed for the used of injection blow molding of pressure bottles for coke, and safety enclosure for pill bottles. A third advantage is the ability to mold multiple containers. Many injection blow molding machine use multiple mandrel forming up to 12 hollow parts at one time. Allowances can be made for thicker bottoms and mid sections by increasing the cavity around the mandrel. The parison at the second stage stretch by extending the steel mandrel forcing the plastic to elongate. This elongation stretches and aligns the plastic molecules along the vertical directions of the container. This increases the overall strength of the container.