The present invention relates to a process for producing a thermoformable rigid polyurethane-polyamide foam having a closed-cell content of less than 70%, which comprises mixing (a) an organic polyisocyanate with (b) one or more polymeric compounds having two or more isocyanate-reactive hydrogen atoms, (c) optionally crosslinking and/or chain-extending agents, (d) one or more carboxylic acids having a functionality of 2 or more, (e) a catalyst comprising a Lewis base component, and (f) optionally auxiliaries and additives to form a reaction mixture and reacting this reaction mixture to form the rigid polyurethane-polyamide foam. The present invention further relates to a thermoformable rigid polyurethane-polyamide foam obtained by such a process and also to the use of such a thermoformable rigid polyurethane-polyamide foam for interior lining or engine compartment lining of motor vehicles.