Aluminum foil is a household staple with a peculiar characteristic: it has a shiny side and a dull side. But why? Some argue that the shiny side reflects heat better than the dull side, making it ideal to cover hot food. Others say that the shiny side is better for wrapping food as it is less likely to stick.
However, even if these claims were valid, they are not the reason why foil is sold this way.
The actual reason for the dullness on one side and shininess on the other is due to the manufacturing process. During the final stage, the foil is rolled so thinly that it goes through rollers in pairs. The side that is exposed to the rollers comes out dull, while the side that is pressed against the other layer comes out shiny.
[via Cubby at Home]