Water sorption by plant cuticular membrane isolates, mainly identified as polysaccharides, after selective extraction of the lipid components waxes and cutin was measured over the whole range of water activity. From water sorption isotherm, the strengths of water binding and water clustering were estimated. Data obtained by differential scanning calorimetry and Fourier-transform and near infrared spectroscopy confirmed the existence of water molecules in different macromolecular environments.