The composition of aluminum foil is 98.5% aluminum, with the remainder consisting mainly of iron and silicon to provide strength and puncture resistance. The molten alloy is rolled thin and solidified between large water-cooled chilled rolls. During the final rolling process, both foil layers pass through the rolling mill simultaneously. The side in contact with the polished steel roller becomes shiny; the other side appears dull. It makes no difference which side of the foil touches the food.
The continuous casting method is much less energy intensive and has become the process of choice. When producing thicknesses below 0.025 mm, it is difficult to produce rolls with a fine enough gap to cope with foil specifications and avoid this, as well as reduce tearing, increase productivity and control thickness for the final pass (1 mil), Two sheets are rolled simultaneously, doubling the thickness at the entrance of the rolls. After passing through the rollers, the two sheets are separated, resulting in a foil with a shiny side and a matte side.
The sides that touch each other are matte and the outside is glossy. Matte aluminum foil has a reflectivity of 80%, while glossy embossed foil has a reflectivity of around 88%. Without instrumentation, the difference in thermal performance between the two sides is imperceptible. According to Kirchhoff's radiation law, an increase in reflectivity reduces the absorption and emission of radiation.
Like all metals, aluminum is ductile. That is, when enough pressure is applied, it will be squashed. This is unlike most other solid materials, which break under pressure. The metal can therefore be rolled into extremely thin sheets.
Metals are ductile because their atoms are held together by a large number of shared electrons that can move, rather than by rigid bonding forces between one atom's electrons and the next's, as in most other solids . In fact, it doesn't matter where the metal atoms are relative to each other, so they can be pushed around freely within the sea of electrons.
In aluminum foil factories, they extrude the aluminum into progressively thinner sheets by rolling the aluminum through a pair of steel rollers that move closer together. Household aluminum foil is less than one thousandth of an inch (two hundredths of a millimeter) thick.
To save space for the final roll, they feed the sandwich two slices at a time into the drum. The top and bottom surfaces are in contact with polished steel rollers, resulting in a beautiful and shiny surface. But the inner surfaces of the sandwich are pressed against each other-aluminum against aluminum. Since aluminum is much softer than steel, these surfaces press against each other, leaving a rougher, duller surface when they separate. No matter how you use the foil, it doesn't make any difference.
