Various reactive gas phase treatments have been investigated as Surface functionalization dry processes with the goal to improve the wertability of parylene C films, keeping good optical properties in the visible range. The films were grown on different substrates by chemical vapor deposition with thicknesses ranging from 300 to 1630 nm. The polymer surface was treated under ultra violet (UV) irradiation at 254 nm in reactive atmospheres including He, H(2)O, H(2)O(2), O(2) and ambient air. The UV/O(2) treatment is the most efficient since the water contact angle decreases from 100 degrees to 6 degrees while the transmittance is maintained at 90% in the visible wavelengths. Furthermore it exhibits long life stability. The functionalization mechanism is discussed in relation with previous reports. (C) 2009 Elsevier B.V. All rights reserved.