There has been a long-standing debate about which side of aluminum foil should be facing up when cooking. However, according to multiple sources, including the FDA, it doesnt matter which side of the foil is facing up or down. Both sides of the foil are made of the same material and will perform the same way. The difference in appearance between the two sides is due to the manufacturing process, where the side that comes in contact with the rollers comes out shiny. However, if you are using non-stick foil, you should make sure to use the dull side, since only one side has the non-stick coating applied.