question about aluminum foil
The fact that one side is shinier than the other is an artifact of the manufacturing process. During the last stages of rolling, two layers of foil pass through the rollers together - to reduce the chance of tearing. The side that was in contact with the other piece of foil has a different texture than the outside side.
The shiny side may be a bit more reflective than the other, but probably not enough to make a difference in ordinary home use.