A moisture sorption isotherm can be used to predict the amount of water that a material will hold if it is exposed to air at a certain relative humidity and a certain temperature. This moisture content is dependent on the temperature and the environmental relative humidity, as well as on the composition of the material. Once the moisture sorption isotherms are determined for at least three temperatures, the net isosteric heat of sorption can be calculated from the sorption isotherms
by using the Clausiuse - Clapeyron equation.