Isobutylene-Isoprene is normally abbreviated to IIR, but is normally referred to as Butyl. It is a synthetic rubber developed in the 1940s. It has exceptionally low gas permeability making it ideal for inner tubes and high pressure/vacuum sealing applications. Its very low resilience makes it suitable for shock and vibration damping. Its chemical unsaturation gives it excellent resistance to heat, ozone, and weathering, and also to dilute acids and alkalis. It is not suitable for use in mineral or petroleum based fluids. Typical applications include diaphragms, gaskets, inner tubes, liners, O-rings, seals, speaker surrounds and bottle closures.