A platen (or platten) is typically a flat metal (or earlier, wooden) plate pressed against a medium (such as paper) to cause an impression in letterpress printing.he platen sits between two steel rolls which deliver the moving force to the sanding belt. Sanding heads with a platen are used on finish sanding with papers of finer grits, when the coarser ones are typically used with contact drum type sanding heads. Stock is fed into and out of the machine on a conveyor belt.