NOVELTY - A water vapor barrier film is laminated film formed by coating a clay film (1) on a resin film (2) as base material, and drying. The clay film contains additive containing clay and thermoplastic or thermosetting resin. The weight ratio of clay with respect to total solid is 60-90 wt.% in the clay film. The water vapor barrier film has water vapor transmission rate of less than 3 g/m2/day, volume resistivity of 10 M( Omega ) or more, and permeability coefficient of less than 4x 10-15 cm2second-1cmHg-1 with respect to oxygen gas.    USE - Water vapor barrier film is used for solar cell back sheet (claimed). Uses include but are not limited to organic electroluminescent element, electronic paper, sealing film for electronic device, film for plasma display panel, food packaging, drink wrapping film, pharmaceutical wrapping film, industrial commodity wrapping film, antioxidation film, chemical-resistant film, light emitting diode, protective film for solar cell, and component for optical communication.    ADVANTAGE - The water vapor barrier film has excellent water vapor barrier property, water resistance, weather resistance, flexibility, heat resistance, electrical insulation property and gas-barrier property.    DETAILED DESCRIPTION - A water vapor barrier film is laminated film formed by coating a clay film on a resin film as base material, and drying. The clay film contains additive containing clay and thermoplastic or thermosetting resin. The weight ratio of clay with respect to total solid is 60-90 wt.% in the clay film. The water vapor barrier film has water vapor transmission rate of less than 3 g/m2/day measured by cylinder plate method for 140 hours, volume resistivity of 10 M( Omega ) or more measured in the orthogonal direction, and permeability coefficient of less than 4x 10-15 cm2second-1cmHg-1 with respect to oxygen gas at room temperature. An INDEPENDENT CLAIM is included for manufacture of water vapor barrier film, which involves preparing clay paste containing clay and additive from dispersion medium, applying on flat resin film, removing solvent form the dispersion medium, and heating at 100-200 degrees C.    DESCRIPTION OF DRAWING(S) - The drawing shows a schematic view of solar cell back sheet.    Clay film (1)    Resin film (2)