Extrusion molding creates long continuous products like PVC pipe, straws, and plastic film. These products can then be cut to size. The typical materials used in this process are plastics, metals, and ceramic. Extrusion starts with heating the raw material and feeding it into a hopper. The material is then funneled through a dye cast forming the desired product. The hot die cast is usually given a cold water bath to solidify the form. Sometimes the material cools slowly so an air injection is utilized to help keep the shape of the product. When a plastic sheet is being made the rollers are usually the cooling apparatus. These rollers create the desired thickness of the sheet and are usually set at multiple intervals.