The term poly-in or poly-out is used by manufacturers of thermal lamination film. Lamination film consists of a polyester side and a laminate side. The easiest way to tell if your film is poly-in or poly-put is to simply take a look at your film. The laminate side of the film is cloudy and the polyester side is usually clear and smooth. Most of the time you don't need to know this terminology when ordering your film. The most important thing is the core size and thickness of laminate film when you place the order.