The invention relates to a method for producing seals made of polyurethane, in which (a) aliphatic polyisocyanate, (b) compounds containing at least two isocyanate-reactive groups, (c) catalysts, (d) antioxidants and/or light stabilizers, and, optionally, (e) blowing agents, and (f) auxiliary agents and/or additives are mixed to form a reaction mixture, and the reaction mixture is allowed to complete the reaction to form polyurethane. The seal made of polyurethane has a Shore A hardness of less than 90 and a density of at least 850 g/L. The polymeric compounds having groups reactive toward isocyanate include b1) polyetherols having a functionality of 2 to 4 and a hydroxyl number of 20 to 100 mg KOH/g, b2) hydrophobic polyols having an OH number of less than 180 mg KOH/g and a functionality of greater than 2 to 3, and b3) chain extenders.