In the blow moulding process, molten resins are extruded in the form of a vertical tube, which is clamped between two halves of a mould. This tube is inflated so that it takes on the shape of the mould. It is then cooled, and released as the fully formed container. For larger containers, the molten resins have to be extruded very quickly or it will 'sag' due to gravity. 

This is called intermittent extrusion, which usually only produces one or two containers for each machine cycle. For smaller containers like those for dairy products and fruit juices, there are machines which can produce up to 16 containers at a time. This allows them to process a high quantity of containers to meet the demands of the industry.