Process:   Plastic pellets are fed into a heated cylinder and driven forward by a turning screw which compacts and melts them and forces the melt through a die at the end, creating continuous lengths of shapes with the desired profile. It is a system much like that of a mincing machine except for the addition of heat. Once the plastic shape is formed it is cooled by air or water

Introduced:   First experiments in the 1840s, widely used from late 1930s

Plastics:   any, especially high density polyethylene; polystyrene and polyvinyl chloride; all synthetic fibres

Marks:   None

Tooling cost:   Moderate

Production volume:   High but restricted to minimum order lengths

Uses:   Anything with a constant cross section: fibres; tubing; pipes; sheets; films; cable sheathing; profiles e.g. curtain rails or window frames