The extrusion process basically is continuously shaping a fluid polymer through the orifice of a suitable tool (die), and subsequently solidifying it into a product (extrudate of constant cross section). In the case of thermoplastics, the feed material, in powder or pellet form, is most commonly heated to a fluid state and pumped into the die, through a screw extruder; it is then solidified by cooling after exiting from the die.