Why are there two different sides then?
The difference does not come from special treatment, but from the manufacturing process.
During lamination, two layers of aluminum are pressed simultaneously between rollers to obtain a very thin and strong sheet. The side in contact with the rollers becomes shiny, while the other, in contact with the second sheet, remains more matte.
This is simply a mechanical effect, not a special feature.
In other words: no mystery, just industrial technique.
The only exception is non-stick aluminum.
However, there is one exception.
Some rolls are labeled “non-stick”. In this case, one side has a treatment designed to limit food sticking.
And it's usually the matte side.
Manufacturers indicate this on the packaging. If your roll is marked “non-stick”, check the instructions and place the treated side in contact with the food to benefit from the non-stick effect.
Otherwise, you can continue to package your vegetables, meats or desserts without asking any questions.
Should one side be favored for better cooking?
Some misconceptions suggest that the shiny side reflects more heat. In practice, in a domestic oven, the difference is minimal and imperceptible.
Heat circulates mainly by convection (hot air) and conduction (direct contact with the dish or food), much more than by reflection.
So whether you are preparing a salmon papillote, roasted vegetables or covering a dish to prevent it from browning too quickly, the result will be the same with cooking foil used in either direction.
A quick practical reminder
Even if the side doesn't matter much, a few simple rules allow you to use aluminum foil safely:
Avoid prolonged direct contact with highly acidic foods (lemon, tomato) at high temperatures, as the acidity can slightly alter the metal.
Never use it in the microwave: this causes sparks and can damage the device.
Do not place it in direct contact with the heating elements or the walls of the oven to avoid any risk of overheating.
Following these precautions ensures safe use and optimal cooking.
The next time you unroll your aluminum foil, you can do so with peace of mind: shiny or matte, the choice is yours.
