Why is one side of aluminum foil shinier than the other?
The factory manufactures two sheets of metal simultaneously to ensure the sheets are strong enough to withstand breakage. The side where the foil comes into contact with another layer of foil appears dull, while the other side, which hasn't made contact with another sheet, appears shiny.
“Where the foil is in contact with another layer, that's the 'dull' side,” Reynold's explains. “The 'shiny' side is the side milled without being in contact with another sheet of metal. The performance of the foil is the same, whichever side you use.”
The difference in terms of appearance is only due to the manufacturing process. (Two foils are laminated at the same time, so each foil is in contact with the rolls on one side only — hence the asymmetrical look).
Material makeup: Tin foil was made with thin leaf tin and sometimes combined with lead. Aluminum foil is made from an alloy that is between 92 and 99 percent aluminum. Cost: Aluminum foil is significantly cheaper to make than tin foil. As an added bonus, it's also more efficient and effective.
Misconceptions in the Kitchen
In fact, some cooks wrap potatoes in aluminum foil dull side facing out during baking with the belief that the shiny side reflects heat toward the potato, cooking it faster. This is just not so. When baking potatoes, the aluminum foil performs the same -- shiny side facing in or out.
The idea behind this is that if someone tries to turn the doorknob, the foil will make noise and alert the person inside that someone is trying to enter.
As it turns out, it really does not matter which side of the aluminum foil you use. "Regardless of the side, both sides do the same job cooking, freezing and storing food," Mike Mazza, marketing director for Reynolds Wrap explained to TODAY. The only time it does matter is if you specifically buy non-stick foil.
The answer is that it doesn't matter which side faces up or down when you're cooking with traditional aluminum foil—but if you're working with a specific nonstick variety, which has a protective coating, be sure to use the side recommended by the manufacturer.
Regular and heavy-duty aluminum foil are made of the same material, but there's a key difference: the thickness of the foil. So what? you might be thinking. Where this really matters is when you're using aluminum foil for cooking.
Really it doesn't matter but in theory you're backwards. Let the dull side absorb heat from the oven and transmit it into the food, keep the shiny side as food side to trap heat inside. The only reason there is a shiny side and a dull side is that the manufacturing process causes it.
