The invention relates to a humidifier configured to humidify an aerosol, the humidifier comprising a first water compartment (100) containing water used to humidify the aerosol a second water compartment (300) containing water used to humidify the aerosol an intermediate chamber (200) located between the first and the second water compartment (100, 300), the intermediate chamber (200) comprising an aerosol inlet (210) and an aerosol outlet (220) and providing first boundary surfaces of a passageway (230) through which the aerosol to be humidified passes a first layer (10) permeable to water vapour and impermeable to liquid water, which is located between the first water compartment (100) and the intermediate chamber (200), wherein a section of the first layer provides a second boundary surface of the passageway a second layer (20) permeable to water vapour and impermeable to liquid water, which is located between the second water compartment (300) and the intermediate chamber (200), wherein a section of the second layer provides a third boundary surface of the passageway (230) opposed to the second boundary surface.
