A novel technique, combining the plasma assisted deposition of SiOx-like coatings with the initiated chemical vapor deposition (iCVD) of organosilicon films in a single-chamber process, was investigated for the production of multistack barriers against the water vapor permeation. Hexavinyldisiloxane (HVDSO) was used as the film precursor for both kinds of polymerization. iCVD of HVDSO resulted in highly crosslinked and adherent carbon-rich polymer which reduced the substrate roughness of the substrate, thus acting as a primer for the deposition of the denser C-depleted uplayer. The plasma ion bombardment of the C-rich underlayer produced a graded interphase which enhanced the adhesion between the layers and of the multilayer stack to the polymer substrate. The C-rich interlayers effectively decoupled the defects of the C-depleted layers, indeed a barrier improvement factor of 100 over the single C-depleted barrier layer was obtained with a hexalayer structure.