Moisture sorption behaviour of silica gel type B size 3.5 mm at 25°C 1-cycle experiment. Figure 5 shows two isotherms, one obtained by wetting a sample from a dry state and the other obtained by drying a sample from wet state. Water sorption (red) and desorption (blue) isotherms at 25°C measured on silica gel. The moisture content at each water activity is higher during desorption (drying from high moisture content) than adsorption (wetting from low moisture content).