So, now that you know the reason behind the different appearances of the two sides, you're probably wondering if you should use aluminum foil with the shiny side up or down. Quite simply, it doesn't matter. Since the exact same material makes up both sides, they will perform precisely the same way.
Reynold's Kitchen, an aluminium foil manufacturer since 1947, says: "It's perfectly fine to place your food on either side so you can decide if you prefer to have the shiny or dull side facing out." It's simply a result of the manufacturing process. The performance of the foil is the same, whichever side you use.
According to Reynold's Kitchen, the difference in appearance between the two sides of aluminum foil is simply a result of manufacturing and serves no real purpose. Meaning, whether you are cooking your food with the shiny side up or the dull side up, you're doing it right.
"The difference in appearance between dull and shiny is due to the foil manufacturing process," he said. "In the final rolling step, two layers of foil are passed through the rolling mill at the same time. The side coming in contact with the mill's highly polished steel rollers becomes 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 reflective surface will reflect heat and the matte side will reflect less heat . If you're baking or defrosting, the matte side will absorb more radiant heat and reflect less infrared heat while the shiny side will reflect more of both, so it makes more sense to bake and defrost with the matte side facing up.
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 shiny side is face-up on the roll, and the dull side is on its underside. In other words, feel free to use whatever side makes you happy.
The hot foil trick is a magic trick in which the magician places a small piece of tin or aluminium foil in a volunteer's hand, and the foil begins to rapidly increase in temperature until the volunteer has to drop it to avoid scalding their hand, and the foil is reduced to ashes on the ground.
“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.”
Why does household aluminium foil have one dull side and one shiny side? SO THAT the shiny side can reflect the heat on to the item to be cooked, using a long-established scientific principle that shiny surfaces reflect heat and light.