Polyurethane foams of density from 60 g/dm 3 to 150 g/dm 3 in accordance with DIN EN 845 and with Shore A hardness > 70 in accordance with DIN 53505 and with heat resistance (in accordance with page 7, lines 10 to 32 of the German-language version of the Description) of up to 40 minutes at from 180°C to 210°C, characterized in that they are obtainable from the reaction of components composed of a) an isocyanate component composed of i) room-temperature-liquid di- and/or polyisocyanates of the diphenylmethane group with from 28% by weight to 33.6% by weight NCO content b) a polyol component composed of i) from ≥ 60 to 80% by weight, preferably from ≥ 65 to 80% by weight, based on the polyol component, of castor oil and/or derivatives of castor oil ii) diamine and/or polyamine-started alkylene oxides with molar masses from 170 to 4800 g/mol, preferably from 200 to 2000 g/mol, and functionalities from 3 to 8, preferably from 4 to 6 iii) optionally one or more crosslinking agents from the group consisting of alcohols and polyether polyols respectively with molar masses from 92 to 3500 g/mol, preferably from 300 to 2000 g/mol, and functionalities from 2 to 8, preferably from 3 to 6 iv) water v) optionally hydrocarbons as physical blowing agents vi) catalysts vii) foam stabilizers viii) optionally auxiliaries and/or additives, where the quantity used of component a) and b) is such that the index is from 90 to 150, preferably from 100 to 140, particularly preferably from 120 to 130. a) an isocyanate component composed of i) room-temperature-liquid di- and/or polyisocyanates of the diphenylmethane group with from 28% by weight to 33.6% by weight NCO content i) room-temperature-liquid di- and/or polyisocyanates of the diphenylmethane group with from 28% by weight to 33.6% by weight NCO content b) a polyol component composed of i) from ≥ 60 to 80% by weight, preferably from ≥ 65 to 80% by weight, based on the polyol component, of castor oil and/or derivatives of castor oil ii) diamine and/or polyamine-started alkylene oxides with molar masses from 170 to 4800 g/mol, preferably from 200 to 2000 g/mol, and functionalities from 3 to 8, preferably from 4 to 6 iii) optionally one or more crosslinking agents from the group consisting of alcohols and polyether polyols respectively with molar masses from 92 to 3500 g/mol, preferably from 300 to 2000 g/mol, and functionalities from 2 to 8, preferably from 3 to 6 iv) water v) optionally hydrocarbons as physical blowing agents vi) catalysts vii) foam stabilizers viii) optionally auxiliaries and/or additives, where the quantity used of component a) and b) is such that the index is from 90 to 150, preferably from 100 to 140, particularly preferably from 120 to 130. i) from ≥ 60 to 80% by weight, preferably from ≥ 65 to 80% by weight, based on the polyol component, of castor oil and/or derivatives of castor oil ii) diamine and/or polyamine-started alkylene oxides with molar masses from 170 to 4800 g/mol, preferably from 200 to 2000 g/mol, and functionalities from 3 to 8, preferably from 4 to 6 iii) optionally one or more crosslinking agents from the group consisting of alcohols and polyether polyols respectively with molar masses from 92 to 3500 g/mol, preferably from 300 to 2000 g/mol, and functionalities from 2 to 8, preferably from 3 to 6 iv) water v) optionally hydrocarbons as physical blowing agents vi) catalysts vii) foam stabilizers viii) optionally auxiliaries and/or additives,