Hydrophilic sheet-like membrane based on a hydrophobic first polymer selected from the group consisting of aromatic sulphone polymers and also a hydrophilic second polymer, where the membrane has a thickness in the range from 30 to 200 µm, a first surface and a second surface and a supporting layer having a three-dimensional sponge-like network structure, where the supporting layer has a first covering layer on its side facing the first surface and a second covering layer on its side facing the second surface, which are integral with the supporting layer, and the first surface and the second surface have approximately oval or circular openings which pass through the first or second covering layer and communicate with the support layer, where the average diameter of the openings in the surfaces differ by a factor of less than 2, where the three-dimensional network structure of the support layer is made up of thick branches and a pore system having contiguous pores, the major part of the branches has a diameter of at least 0.5 µm at their thinnest point, the pores in the support layer are larger than the openings in the surfaces.Se describe una membrana de hoja plana basada en un primer polímero hidrofóbico del grupo que consiste de polímeros aromáticos y en un segundo polímero hidrofílico, en donde la membrana tiene un espesor en el intervalo de 30 a 200 µm, una primera y una segunda superficies y una capa de soporte que tiene una estructura de red tridimensional como de esponja, en donde la capa de soporte tiene una primera capa de cubierta en el lado de la misma que encara la primera superficie y una segunda capa de cubierta en el lado de la misma que encara la segunda superficie, las capas de cubierta se forman integralmente con la capa de soporte, y en donde la primera y segunda superficies tienen aberturas aproximadamente ovales o circulares que penetran la primera y segunda capas de cubierta, respectivamente, y se conectan a la capa de soporte, en donde el di
