This Is the Real Reason Aluminum Foil Has a Shiny and a Dull Side
If there’s no trick to it, then why, exactly, does aluminum foil have a shiny and a dull side in the first place? Experts at Reynold’s Kitchen say that the difference between the two sides is due to a manufacturing process called milling, during which heat and tension is applied to stretch and shape the aluminum foil. Two layers of foil are pressed together and milled at the same time, because otherwise, it would break.
“Where the aluminum foil is in contact with another layer, that’s the ‘dull’ side,” Reynold’s explains. “The ‘shiny’ side is the side milled without being in contact with another sheet of metal. The performance of the foil is the same, whichever side you use.”
But pay attention if you are using non-stick aluminum foil; in that case, there is a difference between the two sides. Since the non-stick coating is only applied to one side, you’ll want to use the dull side. Side note: There will be a label that designates the “non-stick side” in case you forget.