Blow molding is a cheaper technique compared to injection molding and is usually suitable for high volume manufacturing of one piece products like water bottles. The process begins with feeding plastic pellets to the machine with a hopper or a screw. Plastic then melts and gets shaped like a “parison”, a tube with a hole on one end. The parison is fixed in a mold and is inflated or blown to stick to the mold cavity to form the desired shape and is removed after hardening.
In the other two blow molding methods, molten plastic is injected into a mold to form a parison and is picked and blown by a hot rod afterwards.