Hygroscopy

Hydroscopy is the ability of a substance to attract and hold water molecules from the surrounding environment. This is achieved through either absorption or adsorption with the absorbing or adsorbing material becoming physically 'changed' somewhat, by an increase in volume, stickiness, or other physical characteristic of the material, as water molecules become 'suspended' between the material's molecules in the process. While some similar forces are at work here, it is different from capillary attraction, a process where glass or other 'solid' substances attract water, but are not changed in the process (for example, water molecules becoming suspended between the glass molecules).