Hygroscopy

Hygroscopy is the tendency of a substance to absorb or adsorb water vapor from its surroundings. It can cause materials to gain mass, change texture, or dissolve.

Adsorption: Adsorption is the accumulation of atoms, ions, or molecules on a surface. Hygroscopic uptake can occur when water molecules attach to a material's surface.
Desiccant: A desiccant is a material used to remove moisture from its surroundings. Desiccants exploit hygroscopicity to keep enclosed spaces dry.
Water vapor: Water vapor is water in its gaseous state. It is the atmospheric form of water that hygroscopic substances take up.
Hydrophobicity: Hydrophobicity is the tendency of a surface or substance to resist contact with or interaction with water. It describes resistance to water interaction rather than uptake of atmospheric moisture.
Absorption: Absorption is the incorporation of one substance into the bulk of another. Water vapor can diffuse into a hygroscopic material rather than remain only at its surface.
Silica gel: Silica gel is a porous, amorphous form of silicon dioxide used chiefly as a desiccant. Its porous surface adsorbs water vapor in packaging and storage.
Moisture content: Moisture content is the amount of water present in a material, expressed by mass or proportion. It changes as a hygroscopic substance exchanges water with its surroundings.
Hydrophilicity: Hydrophilicity is the tendency of a substance or surface to interact favorably with water. It concerns affinity for water, which does not by itself establish vapor uptake from air.
Relative humidity: Relative humidity is the ratio of the air's water vapor pressure to its saturation vapor pressure at a given temperature. It helps determine whether a substance gains or releases water vapor.
Hygroscopic powder: A hygroscopic powder is a particulate solid that readily takes up water vapor from air. Powders can cake or clump when hygroscopic particles absorb moisture.

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