A comprehensive study of the gas barrier properties of hybrid organic-inorganic coatings formed by polyvinyl alcohol (PVOH) and Si-SiO2, obtained via sol-gel technique, was carried out. It has been shown that the oxygen, nitrogen and carbon dioxide transfer rates of barrier polymers such as poly(ethylene terephthalate) and oriented polypropylene can be further reduced, by up to two orders of magnitude, with a thin coating (1-2 mu m) of PVOH/Si-SiO2. More notably, it has been observed that the material maintains this feature even after a prolonged contact with water, which is a strong solvent for PVOH. Direct moisture sorption measurements show that silica lowers the water uptake of PVOH and inhibits sorption-induced swelling and plasticization of the polymer. Correlations between the gas transport properties of the hybrid coatings and factors such as the silica content, the type of polymeric substrate, the nature of penetrant and the temperature have been found, providing guidelines for the selection and design of multilayer materials for packaging applications. POLYM. ENG. SCI., 50:144-153, 2010. (C) 2009 Society of Plastics Engineers