The present invention is directed to a process for preparing a porous material, at least compris-ing the steps of providing a mixture (I) comprising a composition (A) at least comprising at least one polyfunctional isocyanate as component (ai) and at least one mineral acid (aa), and a sol-vent (B), reacting the components in the composition (A) obtaining an organic gel, and drying of the gel obtained. The invention further relates to the porous materials which can be obtained in this way and the use of the porous materials as thermal insulation material and as catalysts.