NOVELTY - The humidifier has two inlets for supplying dry gas and moist gas, and two outlets for delivering moistened gas and dehumidified gas. A water transfer medium (6) is arranged between two flow plates (2.1, 2.2) and gas-impermeable during operation. The flow plates comprise channels (3) for gas guide. The channels are extended in a waveform with one of the flow plates in sections in an end face plane of the other flow plate and not positively interconnected with the flow plates in a flat surface plane. Channel structures are inserted as an insert into a frame-shaped base plate.    USE - Humidifier for humidifying process gas e.g. hydrogen and/or oxygen, for a fuel cell of a fuel cell system (claimed) to generate electricity.    ADVANTAGE - The channels are extended in the waveform with one of the flow plates in sections in the end face plane of the other flow plate and not positively interconnected with the flow plates in the flat surface plane, thus producing the humidifier in an inexpensive and efficient manner, operating the humidifier in an accurate manner, and minimizing and/or preventing negative effects of the humidifier. The humidifier prevents the water transfer medium from being damaged.    DETAILED DESCRIPTION - The channel structures are designed as fabric-, knitted fabric-, blooming mill stand, slats and shaft structures. The channel structures are made of plastic deformable materials. The flow plates are made of thermoplastic, elastomeric or duroplastic plastics and corrosion-stable metallic materials. The water transfer medium is designed as a membrane laminate i.e. goretex (RTM: waterproof or breathable fabric) membrane, ion-soaked membrane, ionomer membrane i.e. nafion (RTM: sulfonated tetrafluoroethylene based fluoropolymer-copolymer) or diaphragm, a reinforced membrane and an unreinforced membrane that is provided on supporting medium in a form of fiber paper, fiber multi-ply fabric, non-woven fabric or fiber webs e.g. nature and/or artificial fiber. The flow plates are designed as hooks or clips. An INDEPENDENT CLAIM is also included for a fuel cell system.    DESCRIPTION OF DRAWING(S) - The drawing shows an exploded perspective view of a humidifier module with two flow plates and intermediate water transfer medium.    Flow plates (2.1, 2.2)    Channels (3)    Water transfer medium (6)    Breakthrough part (7)    Graphite fiber paper (10)