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This work shows that the discharges pattern and final length, Lf, of creeping discharges depend on the amplitude and polarity of the voltage, the type of gas (mixture) and pressure similarly as in the case of the materials we investigated previously. Lf is longer when the point is positive than when it's negative; this is likely due to the influence of space charge on the electric field. Lf increases quasi-linearly with the voltage; it's reduced when the pressure is increased. Lf is shorter in SF6 than in CO2 or N2. On the other hand, the increase of SF6 content in SF6-CO2 mixture leads to a significant decrease of Lf. Therefore the addition of small concentration of SF6 in a given gas mixture improve the dielectric strength of insulating structure.