In the extrusion process, plastic pellets or powder (dry-blends) is fed into a heated cylinder where rotating screws homogenise it and squeeze it through a die to give a finished or semi-finished product. Pellets are used in single screw extruders, and powders are used in twin screw extruders. The die is designed to produce the desired shape of the end product.

Extruding can produce soft or rigid items which can be compact or cellular in form. For producing hollow articles, a special tool is required and this process is called extrusion blow moulding. Profiles which require an aesthetic appearance are made by the co-extrusion process, which uses two extruders and a specially shaped die.