Ever wondered why ordinary household aluminum foil comes with a shiny side and a dull or matte side? Think maybe there’s some special reason for a shiny side? Or for the matte side? Life is complex—but aluminum foil is not. Here’s the explanation.

Aluminum foil is made by repeatedly thinning aluminum sheet—finer and finer—using highly polished rollers. It is possible to do this only to a point. That point is just slightly before reaching the desired thickness. Although it is possible to obtain aluminum foil that is shiny on both sides, that foil would not be thin enough for practical, inexpensive use.

If manufacturers tried to continue the process still further, without adjustment, the product would be ruined. A modification in the procedure that lets them thin it still further—running two sheets of foil through the rollers, one atop the other.

The top sheet is pressed from above, resulting in its top surface being shiny, while the bottom sheet is pressed from below, resulting in its bottom surface being shiny. The bottom surface of the top sheet and the top surface of the bottom sheet—pressing against each other—do not get pressed by the roller surfaces. When the two layers are pulled apart, these inside surfaces are dull, or matte.

Enjoy the embedded video that shows how aluminum foil is made.