Gas permeation membranes were prepared by exposing multilayered ceramic substrates to low temperature plasmas of C4F8, CHF3; and CF3-CH2F in the presence of argon as carrier gas. Permeation rates for CO2, N-2 and He were measured and ideal selectivities were calculated from the permeability ratios. The chemical structure of plasma films was investigated by XPS analysis and transmission infrared spectroscopy. Structural analysis was completed with deposition rate, critical thickness and density measurements to determine the crosslinking degree of PPFM films (plasma polymerized fluorinated monomers). Correlations between physicochemical properties and gas permselectivities afforded the opportunity of characterizing the gas permeation process through plasma-treated silica membranes.