MACROPOROUS FILTRATION MEMBRANE

Hydrophilic flat-sheet membrane based on a hydrophobic first polymer from the group consisting of aromatic sulfone polymers and a hydrophilic second polymer, wherein the membrane has a thickness in the range between 30 and 200 μm, a first and a second surface and a supporting layer having a three-dimensional sponge-like network structure, wherein the supporting layer has a first cover layer on the side thereof facing the first surface and a second cover layer on the side thereof facing the second surface, which cover layers are formed integrally with the supporting layer, and wherein the first and second surfaces have approximately oval or circular openings which penetrate the first and second cover layers, respectively, and are connected to the supporting layer, wherein the average diameter of the openings in the surfaces differ by a factor of less than 2, wherein the three-dimensional network structure of the supporting layer is made up of thick branches and a continuous pore system, and the predominant proportion of the branches have a diameter of at least 0.5 μm at the thinnest point thereof and wherein the pores in the supporting layer are larger than the openings in the surfaces.