Abstract: Polyurethane elastomers with reduced gas permeability are prepared by reaction of:a) diisocyanates,b) compounds with a molecular weight of 500 to 10,000 having at least two hydrogen atoms that are reactive towards isocyanates,c) compounds with a molecular weight of 61 to 499 having at least two hydrogen atoms that are reactive towards isocyanates, and optionallyd) further auxiliaries and additives,characterized in thati) the ratio of the isocyanate groups in a) to the sum of the isocyanate-reactive groups in b) and c) is between 1:0.80 and 1:1.05 (isocyanate:isocyanate-reactive), andii) the compound b) contains 3 to 15% by wt.