In this paper we present our results on polymer permeability control by organo-SiO x -layers (Aquacer©, Lipocer© 1 ). The goal of our investigations is to use transparent polymers for optical MEMS-packaging. In contrast to costly MEMS-packages made of glass, thermoplastic polymers provide high transparency, low costs and good processability. Their main drawbacks regarding their usage for MEMS-packaging are their high thermal expansion coefficient and their high permeability. On this account, a transparent gas barrier coating with high tolerance against thermal expansion is needed. The organic content in the investigated silicon-oxide-layers induces higher ductility and therefore reduce crack susceptibility in comparison to inorganic silicon-oxide.