Process for producing thin porous membranes having layer thicknesses from 1 μm to 10 000 μm, comprising thermoplastic silicone compound S, wherein a first step comprises forming a solution or suspension from silicone composition SZ which contains alkenyl-containing thermoplastic silicone elastomer S1, alkenyl-containing silicone compound S2 and crosslinker V, in a mixture of solvent L1 and solvent L2, where solvent L1 is easier than solvent L2 to remove from the solution or suspension prepared in the first step from silicone composition SZ and where the maximum concentration of silicone composition SZ attainable in solvent L1 is higher than the maximum concentration of silicone composition SZ attainable in solvent L2, a second step comprises introducing the solution or suspension into a mould, a third step comprises removing solvent L1 from the solution or suspension until the solubility of silicone composition SZ in the mixture of solvent L1 and solvent L2 is forfeited to form a phase A, which is rich in silicone composition SZ, and a phase B, which is lean in silicone composition SZ and hence to effect structure formation by said phase A, and a fourth step comprises removing said solvent L2 and residues of solvent L1, and subjecting the silicone composition SZ to a crosslinking reaction to form silicone compound S, wherein said thermoplastic silicone elastomer S1 utilizes organopolysiloxane/polyurea/polyurethane/polyamide or polyoxalyldiamine copolymers of general formula where structural element E is selected from the general formulae (Ia - f) where structural element F is selected from the general formulae (IIa - f) where R 3 represents substituted or unsubstituted hydrocarbon radicals which may be interrupted by oxygen or nitrogen atoms, R H represents hydrogen or has the meanings of R 3, X represents an alkylene radical of 1 to 20 carbon atoms where mutually non-adjacent methylene units may be replaced by -O- groups, or an arylene radical of 6 to 22 carbon atoms, Y represents a divalent optionally fluorine- or chlorine-substituted hydrocarbon radical of 1 to 20 carbon atoms, D represents an alkylene radical of 1 to 700 carbon atoms which is optionally substituted by fluorine, chlorine, C 1 -C 6 alkyl or C 1 -C 6 alkyl ester and in which mutually non-adjacent methylene units may be replaced by -O-, -COO-, -OCO-, or -OCOO- groups, or an arylene radical of 6 to 22 carbon atoms, B and B' each represent a reactive or non-reactive end group attached to the polymer by a covalent bond, m represents an integer from 1 to 4000, n represents an integer from 1 to 4000, g represents an integer of not less than 1, h represents an integer from 0 to 40, i represents an integer from 0 to 30, and j represents an integer above 0, with the proviso that at least two R 3 radicals per molecule contain at least one alkenyl group and where the silicone compound S2 has a composition of average general formula R 1 a R 2 b SiO (4-a-b)/2, where R 1 represents a monovalent, optionally halogen- or cyano-substituted C 1 -C 10 hydrocarbon radical which contains aliphatic carbon-carbon multiple bonds and is optionally attached to silicon via an organic divalent group, R 2 represents a monovalent, optionally halogen- or cyano-substituted C 1 -C 10 hydrocarbon radical which is free of aliphatic carbon-carbon multiple bonds and is attached via SiC, a represents such a non-negative number that every molecule contains not less than two R 1 radicals, and b represents a non-negative number such that (a+b) lies in the range from 0.01 to 2.5. R 3 represents substituted or unsubstituted hydrocarbon radicals which may be interrupted by oxygen or nitrogen atoms, R H represents hydrogen or has the meanings of R 3, X represents an alkylene radical of 1 to 20 carbon atoms where mutually non-adjacent methylene units may be replaced by -O- groups, or an arylene radical of 6 to 22 carbon atoms, Y represents a divalent optionally fluorine- or chlorine-substituted hydrocarbon radical of 1 to 20 carbon atoms, D represents an alkylene radical of 1 to 700 carbon atoms which is optionally substituted by fluorine, chlorine, C 1 -C 6 alkyl or C 1 -C 6 alkyl ester and in which mutually non-adjacent methylene units may be replaced by -O-, -COO-, -OCO-, or -OCOO- groups, or an arylene radical of 6 to 22 carbon atoms, B and B' each represent a reactive or non-reactive end group attached to the polymer by a covalent bond, m represents an integer from 1 to 4000, n represents an integer from 1 to 4000, g represents an integer of not less than 1, h represents an integer from 0 to 40, i represents an integer from 0 to 30, and j represents an integer above 0, with the proviso that at least two R 3 radicals per molecule contain at least one alkenyl group and where the silicone compound S2 has a composition of average general formula R 1 represents a monovalent, optionally halogen- or cyano-substituted C 1 -C 10 hydrocarbon radical which contains aliphatic carbon-carbon multiple bonds and is optionally attached to silicon via an organic divalent group, R 2 represents a monovalent, optionally halogen- or cyano-substituted C 1 -C 10 hydrocarbon radical which is free of aliphatic carbon-carbon multiple bonds and is attached via SiC, a represents such a non-negative number that every molecule contains not less than two R 1 radicals, and b represents a non-negative number such that (a+b) lies in the range from 0.01 to 2.5.