No entanto, o senso comum (que falha com muita frequência) me diz que com os intervalos de temperatura envolvidos, qualquer benefício é marginal, se é que existe.
A única vez que isso pode importar, é se você estivesse tentando aquecer algo ao sol. Então isso pode fazer a diferença.
EDIT: Do The Straight Dope:
The truth is that the shiny side is not treated with a dangerous chemical. Mineral oil is used as a lubricant during the rolling process, some trace of which may remain on the finished foil--but it's not dangerous. The shiny side is shiny because of the way foil is made. During the last pass through the rolling mill, a double thickness of foil is run between the rollers. The side of each sheet that comes in contact with the polished steel rollers comes out shiny. The other side has a matte finish.
TAMBÉM
The official word from the Reynolds aluminum people is as follows: "It makes little difference which side of the Reynolds Wrap aluminum foil you use--both sides do the same fine job of cooking, freezing, and storing food. There is a slight difference in the reflectivity of the two sides, but it is so slight that laboratory instruments are required to measure it."