According to multiple sources, including Reynolds Kitchen, Bacofoil, and Southern Living, both sides of aluminum foil can be used to cook, freeze, and store food, and there is no difference in performance between the two sides. The difference in appearance between the two sides is due to the manufacturing process, where two layers of foil are pressed together and milled at the same time, resulting in one side being shiny and the other dull. However, if you are using non-stick foil, there is a difference between the two sides. The non-stick coating is only applied to one side, so the food should be placed on the non-shiny side. Reynolds Wrap imprints the words "NON-STICK SIDE" onto the non-stick side of the foil to make it easy to identify.