Aluminum foil is produced by rolling sheet ingots cast from molten aluminum, then re-rolling on sheet rolling mills to the desired thickness.
Beta radiation is passed through the foil to a sensor the other side to help maintain a constant thickness in aluminum foil production.
The shiny and dull surfaces result from the final rolling step in the manufacturing process and make no difference when the foil is used.
In foil mills, heavy-gauge aluminum foil is rolled like clothes put through a wringer to get a thinner gauge of foil for consumers.
In the final rolling, the foil is put through the rollers in two layers, so that more foil can be processed at one time.
The side that is in contact with the highly polished steel rollers becomes shiny, and the other side, which touches the other layer of foil, comes out with a dull or matte finish.