Blow molding is a common type of plastic molding. In this process a plastic tubular form, produced by extrusion or injection molding, is used to form the part.

This form, called a parison, is softened inside a mold and then injected with air or other compressed gas. This expands the parison against the sides of the mold cavity, forming a hollow object the size and shape of the mold. Blow molding is often used to produce plastic bottles and containers.