The invention relates to rigid polyurethane foams obtainable by reaction of A) organic or modified organic polyisocyanates or mixtures thereof, B) compounds having two or more isocyanate-reactive hydrogen atoms in the presence of C) optionally further polyester polyols, D) optionally polyetherol polyols, E) optionally flame retardants, F) one or more blowing agents, G) catalysts, and H) optionally further auxiliaries and/or additives, wherein component B) comprises the reaction product of a1) 15 to 40 wt % of one or more polyols or polyamines having an average functionality of 2.5 to 8, a2) 2 to 30 wt % of one or more fatty acids and/or fatty acid monoesters, a3) 35 to 70 wt % of one or more alkylene oxides of 2 to 4 carbon atoms.