NOVELTY - Reinforced polyurethane foam obtainable by mixing (a) polyisocyanates with (b) compounds having isocyanate-reactive groups, (c) blowing agent comprising water, and optionally (d) catalyst and (e) further additives, to form a reaction mixture and curing the reaction mixture, is claimed.    USE - The reinforced polyurethane foam is useful: as foam for a structural sandwich component and blades and wings, insulation material for liquefied natural gas tanks, where the blades are rotor blades of a wind power system (claimed), reinforcing foams for load-bearing, stiff areal elements; and in wings of sporting aircraft, such as gliders, or in rotor blades of wind power systems.    ADVANTAGE - The reinforced polyurethane foam has improved elasticity, and exhibits very good mechanical properties such as high compressive strength and modulus, tensile and flexural strength, high shear resistance coupled with high elasticity and low density and high thermal stability. The reinforced polyurethane foam is manufactured in a simple and an environmentally friendly manner.    DETAILED DESCRIPTION - Reinforced polyurethane foam having a density of 50-300 g/l, a density-independent compressive strength of 7.5x 10-4 megapascal (MPa) (l/g)1.6, a density-independent compressive modulus of elasticity of 1.7x 10-2 MPa (l/g)1.7, a density-independent tensile strength of 6.4x 10-4 MPa (l/g)1.6, a density-independent tensile modulus of elasticity of 2.4x 10-2 MPa (l/g)1.7, a density independent flexural strength of 1.25x 10-3 MPa (l/g)1.6, and a density-independent flexural modulus of elasticity of 1.75x 10-2 MPa (l/g)1.7, obtainable by mixing (a) polyisocyanates with (b) compounds having isocyanate-reactive groups, (c) blowing agent comprising water, and optionally (d) catalyst and (e) further additives, to form a reaction mixture and curing the reaction mixture, where the reaction mixture to be cured comprises 1-40 wt.% of hollow microspheres and/or is applied to a porous reinforcing agent (f) capable of forming two-dimensional or three-dimensional networks in the polyurethane foam, the (b) comprise polyetherols (b1), polyesterols (b2), chain extenders (b3) and optionally crosslinkers (b4) and aromatic polyether diols (b5), and a fraction of (b2), (b3) and (b5) that is equal to at least 50 wt.%, based on the total weight of the (b), is claimed. An INDEPENDENT CLAIM is included for a process for producing reinforced polyurethane foam comprising the steps (a)-(e) as above per se.