The decision to give tinfoil two different sides—one shiny, one dull—wasn’t made with professional chefs or recreational bakers in mind. In fact, it’s mostly an inconsequential result of the manufacturing process.
To create tinfoil (or aluminum foil, to be precise), a massive slab of aluminum is repeatedly fed through heated steel rollers until it’s just 5 millimeters thick. At that point, it’s moved to a set of cold rollers for further thinning. But as CulinaryLore.com explains, it’s already thin enough to break during that stage, so manufacturers push through two sheets at a time. When the top of the top sheet and the bottom of the bottom sheet rub against the rollers, they get shiny. Since the bottom of the top sheet and the top of the bottom sheet only touch each other, they stay dull.
Because the shiny side seems more reflective, many people think that side should face up while cooking or baking. And if you’re using a DIY solar oven (or trying to fry an egg outside on a hot day), that makes sense: More sunlight will reflect off the shiny surface, which will transfer more heat to your meal. But most regular ovens heat food through a process called convection, where the air in your oven circulates heat energy from the hot areas (e.g. coils) to the cold ones (your food). In other words, convection ovens don’t care how reflective their contents are.
That said, the shiny-versus-dull discrepancy does matter when it comes to certain special types of aluminum foil. The dull side of Reynolds Non-Stick Aluminum Foil, for example, is coated with a substance that will help keep your food from sticking to it—so you should definitely place your food on that side. As TODAY points out, the dull side of that particular product is printed with the term non-stick so you don’t forget.
Aluminum foil also isn’t just for ovens. From sharpening scissors to scrubbing grills, here are 15 other ways to use your roll.