Cu(In, Ga)Se2 (CIGS) solar cells have been fabricated on different metal foil substrates. Preferred foils with regard to costs and physical properties were stainless steel, titanium and Kovar® (Fe/Ni/Co alloy). SiOx films prepared by PECVD and sol/gel methods were deposited as barrier layers on these metal foil substrates. Both film types showed good suitability as diffusion barriers for substrate elements. In the SiOx:Na (sol/gel) barrier sodium could be incorporated to provide the Na-supply to the CIGS absorber. With relatively low sodium concentrations in these films (6% Na2O) large amounts of Na in the absorber have been found. Using a combination of SiOx (PECVD) and SiOx:Na (sol/gel) layers AM 1.5 cell efficiencies of 13.1% on titanium foil substrates have been achieved. With a newly implemented insulation test based on electrolysis measurements pinholes in the barrier layers could be localized and conclusions on their origin could be drawn.