Flame resistant rigid foams and formulations for the production thereof

A rigid polyurethane foam obtained by reacting

• a) an isocyanate group-containing component, with
• b) a component having a flashpoint according to DIN EN 22719 below 55° C., comprising
• b1) at least one substance which is inert toward an isocyanate, does not have an ozone-destroying effect, and has a boiling point below 100° C.,
• b2) a reaction product of at least one compound having an aromatic ring, at least one aldehyde or ketone and at least one primary or secondary amine,
• b3) optionally, at least one isocyanate-reactive component which contains polyester groups,
• b4) optionally, at least one compound which is capable of reacting with the isocyanate and does not correspond to component b2 or b3, and
• b5) optionally, at least one additive required for the production of a foam.