Abstract: A device for humidifying the useful space of a climatic chamber, the humidifying device having a flexible bag which defines water-holding reservoir defined by watertight walls. The flexible bag can be refilled through a closure. The flexible bag is at least partly made of a water-vapor-permeable material, such as a copolymer of tetrafluorethylene and hexafluoropropylene, or polypropylene. The efficiency can be improved compared with conventional open humidifying systems by appropriately structuring the surface of at least the water-vapor-permeable part of the humidifying bag, for example, by providing tufts. To impart form stabilization to the bag, its opposite faces can be joined to each other through the inside of the bag by heat-sealing or stitching.