Which side of aluminum foil should contact food？

Unroll a roll of aluminum foil paper, and you will find that one side is bright and the other is matte. People always think  which side should contact the food, does factory produce the difference intentionally? 

The answer will suprise you: you can use any side to contact food and this is naturally generated in the manufacturing process, not intentional.

Aluminum foil for food, also known as tin foil, is actually made of aluminum. To make aluminum foil paper, you need to grind aluminum into thin sheets. To reach the thickness of paper micron level, the aluminum sheet has to be rolled repeatedly between multiple rollers (rollers).

When the aluminum sheet becomes thin enough, in order to prevent the aluminum foil from being damaged, the two sheets are usually rolled together. As a result, the aluminum foil will become very smooth on the outside which contacts the roller, while the inner surface that does not directly contact the roller will be relatively rough.

Generally speaking, it doesn't matter which side of aluminum foil is used. However, if there is a special coating on one side of the aluminum foil, such as adding an anti-sticking layer (generally on the rough surface), the anti-sticking layer should naturally contact the food to prevent the aluminum foil from sticking to the food. 

The bright side and dark side of aluminum foil paper have different reflective abilities. The bright side reflects more heat, but in fact, the bright side is only slightly brighter than the dark side, and the reflected heat is not much different. The technicians of Shanghai Mengjiang Aluminum Co., Ltd. conducted tests for 48 hours in the laboratory and concluded that the difference between the two sides was very small, and there was almost no difference in cooking time and results.

The microwave oven uses electromagnetic radiation to achieve efficient heating. If aluminum foil is put in, the microwave will be reflected around it, and even sparks will be generated. Therefore, aluminum foil and other metal products cannot be put into the microwave oven.