If i cook with foil I usually use the nonstick reynolds wrap which does have a right and wrong side. It's clearly marked though.

I was told to use the shiny side out and the dull side next to the food as the shiny side has some coating on it that you don't want on your food.

I watched How It's made. They say as stated above there is No difference. It is just the way it comes off the rollers when it is made. Both sides are the same.

so if the sides are the same, why do they look different?

Its the way it comes off the roll at the factory.

I use it in my sewing room for when using heat n bond lite works really good to use shiny side up fabric wrong side up cover with heat and bond and press saves ironing board and fabric comes right up

Here's something else to ponder re: foil. Aluminum has been implicated in Alzheimers'. Since hubby has had 4 family members develop it, we are very cautious about things that contribute to it and needless to say avoid if at all possible, so when I use foil, I first wrap the food in parchment paper or if covering a dish I lay a piece of parchment on the food then the foil. Just enough to prevent the foil from touching the food.