NOVELTY - A polymeric substrate (S1) is produced by depositing first layer of inorganic material on polymeric substrate with largest thickness of at least 100% of Rt-value of polymeric substrate; and depositing second layer of inorganic material on first layer, where in the treatment space the oxygen has concentration of greater than or equal to 3%, and power supply is controlled to provide energy across gap between the two or more opposing electrodes of greater than or equal to 40 J/cm2. The Rt value is the maximum peak to valley height of profile of polymeric substrate measured substantially perpendicular to surface of polymeric substrate.    USE - Method is used for producing a polymeric substrate (S1) used in OLED or photovoltaic cells (claimed).    ADVANTAGE - The method allows control of generation of specific species in gas composition used in atmospheric pressure glow discharge plasma, thus enabling controlled reactant processes in plasma, by which deposition of inorganic layers on polymeric substrate can be achieved under less restricted control as previously reported in prior art for instance due to formation of dust.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) a plasma treatment apparatus (10) which comprises at least two opposing electrodes (2, 3) and treatment space (5) between the opposing electrodes; and    (2) a polymeric substrate having dual layer barrier provided on its surface, in which first layer comprises inorganic buffer layer having silicon-, oxygen-, and carbon-content, and second layer comprises inorganic barrier layer of silicon dioxide.    The two electrodes are connected to plasma control unit (4) for generating atmospheric pressure glow discharge plasma in treatment space, and gas supply device (8) arranged to provide gas mixture in treatment space in operation. The plasma control unit and gas supply device are arranged to execute above method    DESCRIPTION OF DRAWING(S) - The drawing is schematic view showing a plasma treatment apparatus.    Electrodes (2, 3)    Plasma control unit (4)    Treatment space (5)    Gas supply device (8)    Plasma treatment apparatus (10)