Water sorption characteristics are determined for many materials normally by studying weight changes after a sample has been exposed to salt solutions of established relative humidities (e.g. COST 90 procedure).

An established technique (dynamic vapour sorption (DVS)) uses a  microbalance and controlled gas flow to measure water sorption.

The water content of a material can be plotted against its water activity or the relative humidity it was exposed to producing a sorption isotherm. Hysteresis is often observed due to different adsorption/desorption characteristics of the material.

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