How is ISO 811 hydrostatic head measured on zipper tape?

Q: How is ISO 811 hydrostatic head measured on zipper tape?

ISO 811 measures the water pressure at which water penetrates a fabric. The specimen is clamped over a defined test area, commonly 100 square centimetres, and water pressure is raised on one side at a controlled rate, either slowly or quickly depending on the method chosen. The operator watches for the third drop of water appearing on the other face and records the pressure at that moment.

For a zipper, the interesting specimens are the plain tape, the tape with the coil or teeth, and the tape joined to the garment with the seam and the seam tape in place. Condition the samples in the standard atmosphere, avoid handling the test area, and keep the water temperature controlled. Rate of pressure rise, water temperature and the area are fixed by the method, so refer to the standard text.

Report the result in millimetres or centimetres of water column, with the exact specimen construction. A tape result that is much higher than the assembled-seam result is normal; the garment's water resistance is governed by the weakest path, so judge the assembled specimen.