The oxygen barrier properties of sol-gel derived inorganic-organic polymer coatings were investigated. By systematic variation of the ratios of the starting compounds and of the curing conditions, materials with different inorganic and organic network densities were obtained. The network densities were characterized using 29Si solid-state NMR and FT-Raman spectroscopy. It was found that the oxygen transmission rates decrease with increasing inorganic as well as organic network density.