Abstract: The invention relates to a method for drying substances sensitive to being moisturized by a solvent, which mainly consists in separating said substances from a surrounding atmosphere in which said solvent is present, by hermetically sealing said substances in an envelope advantageously having a wall region which does not adhere to said substances and in which said envelope essentially consists of a polymer membrane which is selectively permeable to the vapor of the humidifying solvent but excludes said solvent in the liquid state. The method according to the invention can also be used to prevent dry products from being humidified.