The present invention relates to a reinforced polyurethane foam having a density of above 50 to 300 g/L, a density-independent compressive strength of above 7.5*10-4 MPa (L/g)1.6, a density-independent compressive modulus of elasticity of above 1.7*10-2 MPa (L/g)1.7, a density-independent tensile strength of above 6.4*10-4 MPa (L/g)1.6, a density-independent tensile modulus of elasticity of above 2.4*10-2 MPa (L/g)1.7, a density-independent flexural strength of above 1.25*10-3 MPa (L/g)1.6, and a density-independent flexural modulus of elasticity of above 1.75*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% to 40% by weight 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 compounds having isocyanate-reactive groups (b) comprise polyetherols (b1), polyesterols (b2), chain extenders (b3) and optionally crosslinkers (b4) and aromatic polyether diols (b5), and component (b) comprises a fraction of polyesterols (b2), chain extenders (b3) and aromatic polyether diol (b5) of at least 50% by weight, based on the total weight of component (b). The present invention further relates to a process for producing such reinforced polyurethane foams and to their use as reinforcing foams for load-bearing, stiff areal elements, in the interior of blades or wings, and also as insulation material for liquefied natural gas tanks.