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During the testing of water vapour permeability of fabrics by direct cup gravimetric method, vapour passes through the air gap above the water level in the cup, then it passes through the tested fabric, and finally it must overcome the convection boundary layer above the tested fabric. The evaporation resistance of the air gap reduces substantially the water vapour flow, moreover, the air gap thickness increases with the time of measurement. In this contribution, imperfections of this testing method are discussed. It is concluded that at the end of the direct cup gravimetric test the total evaporation resistance might be 3 times higher then evaporation resistance of the tested fabric. That is why in some countries this method was abandonned. The original inverted cup method with convection moisture transfer along the free surface of the tested fabric employs the semipermeable membrane at the bottom of the inverted cup, which keeps the water inside the cup. An uncertainty of this method is the velocity of air, which passes along the fabric surface. Here, the evaporation resistance of the boundary layer decreases with the square root the air velocity. The related testing standard does not care about the air velocity devations. The novel inverted cup method is based on the placement of the tested sample between two PTFE semipermeable membranes. Outer surface is plunged into liquid water and the inner surface is exposed to the water vapour absorption force of dry potassium acetate, sealed with the sample in the inverted cup. The advantage of this method is the zero dependence of the measurement results on the velocity of the outside air.