Q: What hydrostatic head should a waterproof zipper achieve?
There is no single number, because the requirement comes from the garment's intended use and from the customer's specification. Light rainwear is commonly specified in the low thousands of millimetres, general outdoor jackets higher, and expedition or watersports garments higher again. The zipper should be specified to match the shell fabric rather than to a generic figure, and the assembled seam is the value that matters.
Ask for the hydrostatic head of the tape, of the tape with the chain, and of the taped seam, because film lamination, coating weight and seam sealing all change the result. Also ask how the specimen was prepared: a test on a flat tape can look excellent while the same tape over the slider fails. Test after the wash cycles the care label claims, since coatings and films can degrade.
Acceptance should be written as a minimum for the assembled specimen, tested to ISO 811 at the agreed rate, with a stated number of specimens and a rule for the lowest value. Where a customer quotes a figure without a method, ask which specimen and which rate were used before agreeing to it.