The other day I was wrapping some food to put into the freezer. I noticed, as I have noticed before, that the aluminum foil that I was using for that purpose had one side that was decidedly more shiny than the other. But this time, that idle moment of recognition was followed by curiosity, and a question: when I wrap food, am I supposed to be distinguishing between the super shiny and less shiny sides and intentionally making sure that one side, or the other, is the inner side or outer side when the wrapping is done? In short, have I been doing things wrong for all these years by paying absolutely no attention to the sides of the foil and wrapping food randomly?
I checked the Reynolds Wrap box, which I’ve never read before, to see whether it has an instructions area. After all, manufacturers tend not to be shy in telling you the best way to use their products; in fact, you might say that product boxes are often pretty bossy about it. The Reynolds Wrap box says you can use the wrap to cover food and prevent “freezer burn,” use it to line pans before cooking, and cover bowls that are being put into the refrigerator to help keep the contents moist and avoid splatters. The box even offers tips about inventive uses of Reynolds Wrap, such as covering open ice cream with the foil to prevent formation of ice crystals, or shaping the foil into little cups to start seedlings or to hold nuts or candy. But there is nary a word about making sure to keep the shiny side against the food being wrapped.
Nevertheless, a debate rages on the internet. Some people feel strongly that the mirror-like side of the foil must always be on the interior next to the food, reasoning that the shiny side will reflect more of the radiant heat. You can read an exhaustive treatment of the subject here, which concludes that there really isn’t much difference in heat reflection. But the heat reflection analysis doesn’t make much sense to me in any case, in view of the fact that most uses of aluminum foil occur when you are putting something into the fridge or the freezer–in which case you wouldn’t care one whit about reflecting the radiant heat and in fact would want to take steps to cool or freeze the food being wrapped as quickly as possible. On the other hand, if you were using the aluminum foil to shape into little cups to hold M&Ms for a kid’s birthday party, you’d want to have the shiny side up to make for a more festive and color-reflective presentation.
In short, my effort to inform and potentially correct my aluminum foil usage came to naught. I’m convinced there is no difference, other than in the M&M cup context, with manufacturer silence on the topic being the deciding factor. So when you’re wrapping food for the freezer, feel free to place either side against the food according to your fancy at the moment.