Foil (metal)
A foil is a very thin sheet of metal, usually made by hammering or rolling. Foils are most easily made with malleable metals, such as aluminium, copper, tin, and gold. Foils usually bend under their own weight and can be torn easily. The more malleable a metal, the thinner foil can be made with it. For example, aluminium foil is usually about 1/1000 inch (0.03 mm), whereas gold (more malleable than aluminium) can be made into foil only a few atoms thick, called gold leaf. Extremely thin foil is called metal leaf. Leaf tears very easily and must be picked up with special brushes.
Aluminium–lithium alloy
Aluminium–lithium alloys (Al–Li) are a series of alloys of aluminium and lithium, often also including copper and zirconium. Since lithium is the least dense elemental metal, these alloys are significantly less dense than aluminium. Commercial Al–Li alloys contain up to 2.45% by mass of lithium.