Armour (or armor U.S.) is a protective covering or clothing to prevent injury from attack. Armour can be worn by a person, or it can be used to protect machines, animals, even buildings. Armour has always been made from the strongest materials available at the time, but weight has always been a problem. Early body armour was made from leather. Later, metals were used (e.g. mail or plate armour). Some modern armour, like bullet-proof vests, are made from plastics that do not stretch or break, such as Kevlar. These plastics may be woven into a cloth and used in layers, which makes them even stronger.