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The deposition of silicon oxide thin films as diffusion barriers on paper based substrates by means of plasma enhanced chemical vapor deposition has been investigated. Polyethylenetherephtalate film served as reference substrate. A microwave-driven slot antenna plasma source was utilized. To measure the material oxygen permeability a device has been developed which allows to measure in a broader permeability range than commercially available instruments. In addition, it also enables to detect pores in the material surface by varying the total pressure difference between the measuring chambers. It is shown that the existence of persistent pores in the substrate material is in direct relation to the success of a silicon oxide coating in terms of the reduction of the oxygen permeability. If the material possesses a totally sealed surface a reduction of the oxygen permeability in the same order of magnitude as on polymeric webs is possible. [Copyright &y& Elsevier]