Method of making foamed resins with internal mold-release agents

In a process for the production of molded articles of polyurethane foam by foaming a reaction mixture in a closed mold, said reaction mixture comprising an organic polyisocyanate, an organic compound containing at least two hydrogen atoms reactive with said isocyanate, and a blowing agent, the improvement comprising adding to said reaction mixture, a mold releasing amount of the reaction product of

• (a) an organic polyisocyanate and
• (b) from 0.5 to 25% by weight based on the quantity of said component (a), of an active hydrogen containing fatty acid ester prepared by reacting an alcohol with an aliphatic, saturated or unsaturated fatty acid, said ester being characterized in that at least one aliphatic acid which contains more than 8 carbon atoms is built into the molecule, said ester further characterized as having an acid number of 0 to 100 and a hydroxyl number of 0 to 150 with at least one of said numbers being greater than 0, said ester having an average molecular weight of from 500 to 5000.