A method of manufacturing a humidity control device including the steps of: a) providing an envelope in an open configuration; b) introducing in at least one part of the open envelope a given weight of a humidity control agent having a known moisture content lower than the moisture content corresponding to a targeted equilibrium relative humidity level (ERHi); c) introducing a given weight of water in the at least one part of the open envelope; and d) repeating steps b) and c) until a desired weight of hydrated humidity control agent is received in the at least one part of the open envelope.