And of course then I went and got on a train and then went Christmas shopping and left you all* hanging.,,
Foil is made by rolling aluminium thinner and thinner. But it's not possible to get rollers closely enough spaced for the final thinness, because the foil will stick to the rollers, so for the last roll, the foil is folded double, so that it can come out at half the smallest possible gap.
The shiney side is the roller side, and the dull side is the side that's in contact with the other half of the foil.
*checking my post, I found I'd typed al here, not all, which is kinda appropriate for the subject of aluminium....