NOVELTY - Producing a polymer stamp for the reproduction of devices comprising microstructures and nanostructures, comprises providing a thermoplastic foil; providing a first substrate; patterning nanostructures (3) into the thermoplastic foil; patterning microstructures (5, 6) onto the first substrate; covering the first substrate surface comprising the microstructures (5, 6) with the nanostructured thermoplastic foil; casting a polymer elastomer onto the first substrate with nanostructures (3) and microstructures (5, 6) to form a polymer stamp; and releasing the polymer stamp.    USE - The method is used for producing a polymer stamp for the reproduction of devices comprising microstructures and nanostructures (claimed).    ADVANTAGE - The method is for producing a polymer stamp or mold as well as a device from the polymer stamp or mold, in which the nanostructures and microstructures are incorporated into the stamp or mold and are transferred to the final device from the stamp or mold. The passive device for a fuel cell system exhibits hydrophobic and hydrophilic areas in a simplified way at lower costs for separation of gaseous by-products from liquid fuels.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are:    (1) a method of reproducing devices comprising microstructures and nanostructures;    (2) polymer stamp comprising: first microstructures (5) extending along a first direction, second microstructures (6) extending along a second direction different from the first direction, and nanostructures (3) formed at least on one surface of the first and/or second microstructures (5, 6) of the polymer stamp, the nanostructures being provided to extend at least along the first direction, where the nanostructures (3) are patterned into the at least one surface of the first and/or second microstructures (5, 6) and are formed of the same material as the microstructures (5, 6) themselves, where the aspect ratio of a single nanostructure element is larger than 5; and    (3) a device comprising: first microchannels (5) extending along a first direction, second microchannels (6) extending along a second direction different from the first direction, and nanostructures (3) formed at least on the bottom of the first and/or second microchannels (5, 6) and provided to extend at least along the first direction, where the nanostructures (3) are patterned into the surface of the microchannels (5, 6) and are formed of the same material as microchannels (5, 6) themselves where the aspect ratio of a single nanostructure element is larger than 5.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of the final product.    Nanostructure (3)    Microstructures (5, 6)    Through-hole (7)    Final product (12)    Opening (13)