The invention relates to a sealing material, to a gas seal made of this sealing material, and to a method for the production of such a gas seal made of this sealing material. The sealing material contains a bromobutyl elastomer in an amount of 100 parts by weight, a filler material in an amount between 10 and 100 parts by weight for setting the volume of the sealing material, a curing agent in an amount between 0.5 and 3.0 parts by weight for curing the sealing material, and a cross-linking component in an amount between 0.1 and 2.0 parts by weight for bringing about a peroxidic cross-linking of the sealing material. This sealing material permits a particularly high vacuum-tightness (that is to say, a low leakage rate) in comparison to sealing materials according to the state of the art, and accounts for resistance, on the one hand, to aggressive gases and, on the other hand, to pump oils such as, for instance, perfluoropolyethene oil or silicon oil.