Used in Blow Molding processes. Heat-softened polymer (such as PET) is formed into a shape similar to a thick test tube with neck threads. In 2-stage stretch blow molding, the preform is cooled for storage; when it is needed, the tube is re-heated and inflated while inside a Blow Mold to create the shape of the desired bottle or jar. In single-stage injection stretch blow molding, the preform is formed immediately prior to being placed in the blow molding station without cooling down.