Materials include steel (in the form of links or cables), polyurethane, rubber, and fabric. The original-style steel-link chains are also available in a variety of carbon steel and steel alloys and link shapes. Link shapes include standard, twisted, square, and reinforced. The shape of the links changes the flexibility, grip, and strength of the chain. The links can also have added studs or V-bars for an even more aggressive traction. The use of alloy steel and hardened steel adds durability. Traction cables (cable chains, snow cables) attach like chains but are made from cable rather than chain.