Full definition
Isobutylene-isoprene copolymer with exceptionally low gas permeability (8-10x lower than NR) and excellent vibration damping (rebound resilience only 12-20%, lowest of commercial rubbers). Temperature range: -45 to +120°C (standard), +150°C (halobutyl grades). Key properties: outstanding ozone and weathering resistance (nearly saturated backbone), excellent chemical resistance to dilute acids, alkalis, and polar solvents, and high-temperature fatigue resistance. Limitations: poor resistance to hydrocarbon solvents and mineral oils, difficult to co-vulcanize with other rubbers (very low unsaturation), slow cure rate. Halobutyl variants (chlorobutyl CIIR, bromobutyl BIIR) solve the co-cure issue and are essential in tubeless tire innerliners. Applications: tire innerliners and inner tubes (largest use, due to air impermeability), pharmaceutical bottle stoppers, vibration isolation mounts, chemical tank linings, gas masks, and bladders. Per ASTM D2000 classification: AA. Global production: ~1.3 million tonnes/year. Manufacturers: ExxonMobil, Lanxess, PJSC Nizhnekamskneftekhim.