These films are coated on 5 mil polyester. The coating loves water which is the carrier for the ink. The polyester side is very shiny and doesn't absorb water. You can test the film for the coated side by wetting your fingers and pinching the film on both sides. The coated side will get sticky just like capillary film. Ulano cuts a notch in the upper right corner of the coated side so you don't have to test. Rolls are coiled with the coated side out, ready to go into the printer.