Aluminium foil is aluminium prepared in thin metal leaves with a thickness of less than 0.2mm (7.9 mils); thinner gauges down to 4 micrometers are also commonly used. Standard household foil is typically 0.016 mm (0.63 mils) thick; heavy-duty household foil is typically 0.024 mm (0.94 mils). The air conditioner foil can be thinner than 0.0047mm, and some food foil thinner than 0.002mm. The foil is pliable and can be readily bent or wrapped around objects. Thin foils are fragile and are sometimes laminated with other materials such as plastics or paper to make them stronger and more useful. It's used industrially for a variety of purposes, including packing, insulation and transportation. At home, people use aluminium foil for food storage, to cover baking surfaces and to wrap foods, such as meats, to prevent them from losing moisture while cooking.
Aluminium foil is produced by rolling sheet ingots cast from molten billet aluminium, then re-rolling on sheet and foil rolling mills to the desired thickness, or by continuously casting and cold rolling. To maintain a constant thickness in aluminium foil production, beta radiation is passed through the foil to a sensor on the other side. If the intensity becomes too high, then the rollers adjust, increasing the thickness. If the intensities become too low and the foil has become too thick, the rollers apply more pressure, causing the foil to be made thinner. The rolls of aluminium foil are then slit on slitter rewinding machines into smaller rolls. Roll slitting and rewinding is an essential part of the finishing process.