Abstract: A process for making integral skin foams which comprises reacting into a closed mould:A) an organic polyisocyanateB) an isocyanate-reactive composition comprising:(i) a catalytically effective amount of a urethane-promoting catalyst and optionally a urea-promoting catalyst,(ii) a catalytically effective amount of a carbodiimide-promoting catalyst, and(iii) an isocyanate-reactive compound; in the presence ofC) an inert physical blowing agent.The process provides integral skin foams having good skin properties at reduced physical blowing agent levels.