NOVELTY - Reinforced polyurethane foam obtainable by mixing polyisocyanates with compounds having isocyanate-reactive groups, propellants, and optionally catalyst and further additives to form a reaction mixture, and curing the reaction mixture, is claimed. The reaction mixture to be cured comprises hollow microspheres and/or is applied to a porous reinforcing agent, which forms two-dimensional or three-dimensional networks in the polyurethane foam. The compounds having isocyanate-reactive groups comprise polyetherol, polyesterol, chain extenders and optionally crosslinkers and aromatic polyether diols.    USE - The reinforced polyurethane foam is useful: in a sandwich component; and as a reinforcing foam in blades, preferably rotor blades of a wind turbine, and wings, and as an insulation material for liquefied natural gas tanks (all claimed).    ADVANTAGE - The reinforced polyurethane foam: exhibits high compressive strength, high compressive modulus of elasticity, high tensile strength, high flexural strength, high tensile modulus of elasticity, high flexural modulus of elasticity, high shear strength, high elasticity, low density and high temperature resistance; and is easily produced; and can be recycled or disposed in an environmentally friendly manner.    DETAILED DESCRIPTION - Reinforced polyurethane foam having a density of greater than 50-300 g/l, a density-independent compressive strength of greater than 7.5x 10-4 MPa (l/g)1.6, a density-independent compressive modulus of elasticity of greater than 1.7x 10-2 MPa (l/g)1.7, a density-independent tensile strength of greater than 6.4x 10-4 MPa (l/g)1.6, a density-independent tensile modulus of elasticity of greater than 2.4x 10-2 MPa (l/g)1.7, a density-independent flexural strength of greater than 1.25x 10-3 MPa (l/g)1.6, and a density-independent flexural modulus of elasticity of greater than 1.75x 10-2 MPa (l/g)1.7, obtainable by mixing (a) polyisocyanates with (b) compounds having isocyanate-reactive groups, (c) propellants comprising water, and optionally (d) catalyst and (e) further additives to form a reaction mixture, and curing the reaction mixture, is claimed. The reaction mixture to be cured comprises hollow microspheres (1-40 wt.%) and/or is applied to a (f) porous reinforcing agent, which forms two-dimensional or three-dimensional networks in the polyurethane foam. The compounds having isocyanate-reactive groups (b) comprise (b1) polyetherol, (b2) polyesterol, (b3) chain extenders and (b4) optionally crosslinkers and (b5) aromatic polyether diols. The fraction of components (b2), (b3) and (b5) in component (b) is at least 50 wt.%, based on the total weight of component (b). An INDEPENDENT CLAIM is also included for producing reinforced polyurethane foam, comprising mixing component (a) with components (b), (c), (d) and (e) to a reaction mixture and curing the reaction mixture.