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 uniform profile. 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.