disclosed are expandable bladders for use in curing presses for rubber compositions such as pneumatic tires . the bladders are a crosslinked elastomer comprising an isobutylene rubbery polymer . the bladder composition includes corn oil which improves the release characteristics of the cured bladder from a tire innerliner cured in contact with said bladder . the improved release characteristics have been observed to allow rubber compositions such as tires to be molded with fewer defects caused during release of the bladder from the tires or caused by abraded or deformed bladders . the use of corn oil also has been observed to increase the useful life time of the bladder allowing more tires to be cured without changing bladders . a preferred isobutylene rubbery polymer is a brominated copolymer of isobutylene and p - methylstyrene . the bladder compositions have also been observed to have an enhanced flexibility due to the corn oil .