Abstract: A device for regulating the relative humidity of a closed chamber includes a layer of material capable of being impregnated with liquid and of adsorbing or desorbing vapor of the liquid. The material has on one of its surfaces a membrane which is permeable to vapor but not to liquid. The membrane having an outer surface which is hydrophobic. The adsorbent/desorbent material can be arranged in a sealed tank with an opening for filling with liquid. The device is especially suitable for a paint palette in a chamber having a cover, so that paint can remain on the hydrophobic surface without drying.