Droplets can roll off a fabric that still lets water through under pressure. For procurement, ask two separate questions: how readily does the outer surface wet, and at what pressure does water pass through the fabric? A water resistance label without a method and result cannot answer both.
What a surface wetting test shows
DWR is a water repellent surface finish. The DWR label alone gives no test rating. ISO 4920 describes a spray test that assesses surface wetting. It does not measure water passing through the material. If your bag specification concerns how readily the outer panel wets, ask for a result from this or another clearly identified surface test. ISO 4920.
What hydrostatic head means
ISO 811 describes testing resistance to water penetration under hydrostatic pressure. A data sheet may express pressure as a height of water column or in pressure units such as kPa or bar. Match the test method, sample face, loading conditions and condition after preparation or ageing, as well as the units. ISO 811.
How to read the X-Pac VX21 example
For standard VX21, the manufacturer lists DWR in the construction and gives a separate waterproof figure of 13.8+ bar (200+ psi). The plus sign is part of the published value. These data apply to the fabric in that configuration. The product page does not identify the method behind the figure, so do not attribute it to ISO 811 without a test report. X-Pac VX21.
Why seams need a separate check
Water can enter a finished product through a seam, closure or attachment point. After selecting the fabric, test an assembled sample with the planned seam and components. Specify the direction and duration of water exposure and agree what counts as a leak before testing. If performance after flexing or care matters, repeat the check after the appropriate preparation.
What to include in an enquiry
Give the item code, intended use and what you need to verify: surface wetting, penetration through the fabric or performance of the assembled product. Ask for the method, unit, result and test conditions. If the documentation is incomplete, agree on a sample test before ordering for production.
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