According to Reynolds Metals, makers of Reynolds Wrap® Aluminum Foil, "the difference in appearance between dull and shiny is due to the foil manufacturing process. In the final rolling step, two layers of aluminum foil are passed through the rolling mill at the same time. The side coming in contact with the mill's highly polished steel rollers becomes shiny. The other side, not coming in contact with the heavy rollers, comes out with a dull or matte finish."