Extrusion is a process that forces plastic or molten material through a shaped die under pressure to form various products like thin films, tubing, pipes, and profiles. Common materials that are extruded include nylon, polyethylene, polypropylene, and polyvinyl chloride. The extrusion process involves feeding material into a hopper, melting it, forcing it through a die, cooling it with rollers, and cutting it to final lengths or widths. Sheet thickness is controlled by the speeds and sizes of the extruders delivering the materials, while cooling is achieved through rollers over a set number of passes to adequately dissipate heat without creating defects. Calendering may also be used to force the mol