Whether you’re roasting bell peppers, oven-steaming fish, or baking a batch of blondies, you need a trusty roll of aluminum foil to help you get the job done. So many recipes call for foil that you may not even think twice about it as you dash off yet another sling for your pan—but we wondered if there’s a right and wrong way to use it. Foil has a shiny side and a dull side, and we tend to use the two sides interchangeably in the kitchen: But what if one side is better than the other?
Sign up for the Cook's Insider newsletter
The latest recipes, tips, and tricks, plus behind-the-scenes stories from the Cook's Illustrated team.
To get some answers, we reached out to Reynolds Consumer Products. A representative of the company told us that foil’s shiny- and dull-sidedness is simply the result of the manufacturing process—and that there are no performance differences between the two sides. The only exception? If you’re using a nonstick foil, which may only be nonstick on one side.
But of course, we wanted to test this out for ourselves. We conducted three experiments, each designed to prove or disprove the negligibility between foil’s two sides. Here’s what we found out.
The Potato Test
THE EXPERIMENT: We baked two potatoes, each of exactly the same weight, in a 350-degree oven, one wrapped in foil with the shiny side facing out and the other with the shiny side facing in.
THE RESULT: After one hour, both potatoes reached an internal temperature of 198 degrees.
The Water Test
THE EXPERIMENT: We filled two ovensafe beakers with 71-degree water and wrapped each in foil, one, shiny side out, the other, shiny side in.
THE RESULT: After 30 minutes in a 350-degree oven, the water in the beaker wrapped in foil with the shiny side in was 2 degrees hotter.
The Leftovers Test
THE EXPERIMENT: We baked cold mashed potatoes in two eight-by-eight glass baking pans covered in foil, one with shiny side out, the other, shiny side in.
THE RESULT: After 45 minutes, the pan with the shiny side facing in was 2 degrees hotter.
With that, we felt confident concluding that it’s true that the two sides of foil are pretty much interchangeable. Which is great news: Less time thinking about which side of the foil to use means more time to decide what to cook in it.