Blow molding is the manufacturing process that allows resins, plastics and polymers to be formed into shapes with hollow and internal cavities that a mold would not be able to be removed from. This process is most commonly seen in plastic bottles. The process works by placing a small preform or tube onto a nozzle like end that then heats the preform, at the same time air is blown into the preform and it expands the heated material to the shape of the surrounding mold.