Poly(vinylidene chloride-co-acrylonitrile) (P(VDC-co-AN))/silica hybrid composite systems were successfully prepared by the sol-gel method using an appropriate coupling agent and solvent system (1:1 ratio of THF - tetrahydrofuran and NMP - N-methyl-2-pyrrolidone) to enhance their water vapor and oxygen barrier properties while maintaining their coating transparency. A silane coupling agent consisting of 3-glycidyloxypropyltrimethoxysilane (GPTMS) was used to suppress the phase separation between the P(VDC-co-AN) and inorganic SiO2. The gas permeabilities of the hybrid composites were minimized by adding the silica component in the range of 10-20 wt%, and a thin coating at ca. 1-2 mu m lowered the permeabilities of oxygen and water vapor to 2.88 x 10(-10) ml mm m(-2) s(-1) GPa(-1) and 1.12 x 10(-5) g mm m(-2) s(-1), corresponding to improvements of 94.14% and 25.38%, respectively, compared to that of the pristine PET film. The optical transmittance of the hybrid coating was over 85% in the visible range (380-800 nm) and the surface roughness was less than 86.3 nm. (C) 2009 Elsevier B.V. All rights reserved.