Plastics extrusion commonly uses plastic pellets, which are fed into a hopper and subsequently to a feed screw section. The polymer resin moves by a rotating screw, heated to the molten state by a combination of external and shear heating. The screw forces the resin to flow through a shaping die, forming the resin into the desired shape. The extrudate exiting a forming die is cooled and solidified. A variety of polymers is used to produce plastic profiles such as tubing, large pipes, rods, rails, sheets and films.