Extrusion blow molding is a manufacturing process used to produce hollow parts that range in size from large septic tanks to small eye-drop squeeze bottles. Using a process derived from the glass blowing industry, a molten open-ended tube of resin (called a parison) is extruded through an annular die and captured between two mold halves as they close. Mating surfaces on the mold pinch together the open areas of the tube and high pressure air is introduced inside the captured tube, inflating it to conform to the shape of the inside of the mold.
In this manner, blow molded parts, including bottles for detergents, bleach, household cleaners and food products (including milk, juice, and water) are economically produced. While high density polyethylene is the largest volume thermoplastic used in extrusion blow molding, parts are routinely made from polypropylene, LLDPE and LDPE.