hygroscopic

Said of a body or substance, having the capacity to absorb water vapor from the air surrounding it. The condensation nuclei around which cloud droplets begin to grow are also known as hygroscopic nuclei, given their capacity to trap water vapor from the environment in which they float. Condensation of the aforementioned gas on their irregular surface gradually forms a film of water; that little film fattens quickly if the tiny particle evolves in a favorable environment, saturated with moisture.