Polymer Industries utilizes compression molding to produce its UHMW sheets and thick gauge HDPE, PP, HMW, and LDPE. UHMW is a material that does not flow when it melts, therefore it has to be either ram extruded or compression molded. Compression molding is a process by which material is placed inside of a metal mold that is in the form of a sheet. This mold is placed inside of the press which presses the material under heat and pressure so it will take the form of a sheet. After the sheet comes out of the mold, the sides of the sheet are trimmed so that edges have a good finish. Sheets are either sold as is with a thickness tolerance of 10% or planed to the desired thickness. Compression molding is utilized for HDPE, PP, HMW, and LDPE sheet for thicknesses of 1 1/2" and above. These materials are not able to be extruded at this thickness and must be molded to be made.