TECHNOLOGY FOCUS - POLYMERS - Preferred Components: The reinforcing agents are glass fiber mats. The layers of the reinforcing agent are homogeneously distributed in the foam. The compounds containing isocyanate-reactive groups (b) contain a polyetherol (b1) having a functionality of greater than or equal to 4 and a viscosity at 25 degrees C of less than or equal to 10000 mPas and a polyetherol (b2) having a functionality of less than or equal to 3.5 and a viscosity at 25 degrees C of 600 mPas. The compounds containing isocyanate-reactive groups (b) next to the polyetherol (b1) and the polyetherol (b2) contain a polyesterol (b3) having a viscosity at 25 degrees C of less than or equal to 2000 mPas, chain extender (b4), and optionally a crosslinker (b5). The rigid polyurethane foam contains polymeric methylenediphenyl-diisocyanate as an isocyanate component. The rigid polyurethane foam has a density of 30-500 g/l. The rigid polyurethane foam has a density-independent compressive strength of at least 5x 10-4 (preferably at least 5.5x 10-4) MPa (l/g)1.6. The rigid polyurethane foam exhibits a dense pressure-independent modulus of elasticity of at least 8x 10-3 (preferably 9.5x 10-3) MPa (l/g)1.7. Preferred Process: The rigid polyurethane foam is manufactured by mixing (a) polyisocyanates, (b) compounds containing isocyanate-reactive groups, (c) propellant containing water, (d) a catalyst mixture comprising tertiary amines and optionally (e) other additives, to a reaction mixture, applying the reaction mixture to a reinforcing agent and curing the reaction mixture. The coating agent is a compact, polyurea, which is obtainable by mixing compounds with at least two isocyanate groups with compounds having at least two primary or secondary amines. The polyurethane foam is coated by spraying a reaction mixture to produce a compact polyurethane or a compact polyurea on the rigid polyurethane foam. The reaction mixture for the production of a compact polyurethane or a compact polyurea is sprayed to parts or the entire inner surface of a mold and then the reinforcing agent and the reaction mixture for the production of rigid polyurethane foam react into the mold.