Elastomers, also known as rubbers, are polymers that are elastic and flexible. They have low Young's modulus and high failure strain compared to other materials. Elastomers exist above their glass transition temperature, allowing considerable segmental motion. Common elastomers include natural rubber and synthetic rubbers like polyisoprene, butadiene rubber, nitrile butadiene rubber, chloroprene rubber, thermoplastic elastomers, fluoroelastomers, and silicones. Elastomers are usually thermosets that require vulcanization, but can also be thermoplastics. They are characterized by large elastic elongation, the ability to stretch and return to their original shape, and flexibility.