The material of a part includes a composition obtained by blending an isobutylene-based, pre-crosslinked polymer as component (A), at least one poly olefin or a non-crosslinked rubber or a TPV as component (B), at least one polymer having a Tg of 90° C. or higher as component (C) and—preferably—at least one component (D) selected from the group of: substituted vinyl polymers, stryrenic block copolymers, inorganic functionalized and non-functionalized fillers, carbon black, halogen scavengers, preferably the inorganic halogen scavengers, acid acceptors, stabilizers, preferably the polymeric stabilizers, and processing aids. Also, a method of manufacturing such part includes the steps: a) Pre-mixing at least one substance representing component B, with at least one substance representing component C and at least one substance representing component D； b) compounding the obtained premix with component A and optionally a further portion of component B or D； and c) molding the resulting composition of step (b) into a pharmaceutical seal. Also, a method of radiation sterilization a part, e.g. a pharmaceutical closure, the part being produced from compounds based on thermoplastic vulcanizates including isobutylene monomer units, prior to irradiation, packs the parts under an inert atmosphere in a container impermeable to oxygen, wherein the packed closure materials are irradiated for sterilization.
