To understand what an extruder is, we must first know what the process of extrusion is. Extrusion is when a material, usually pellets, dry powder, rubber, plastic, metal bar stock or even food is heated and pushed through a die. A die is essentially a mold that shapes the material as it is forced through the small opening to the other side. It’s one of the most common ways to produce sheets and strips of stock metal, plastic and rubber shapes. http://www.huachu-machine.com/film-blowing-machine/aba-three-layer-film-blowing-machine/