(1) Process in which fluid molecules are concentrated on a surface by chemical or physical forces or both; (2) surface adherence of a material in extracting one or more substances present in an atmosphere or mixture of gases and liquids, unaccompanied by physical or chemical change (from Gatley, Understanding Psychrometrics).

Related terms: Absorption, Hydrophilic, Hydrophobic, Hydroscopic

Related resources: BSD 138: Moisture and Materials, Info-500: Building Materials Property Table, Development of Moisture Storage Coatings for Enthalpy Storage Wallboard