ISO 811

Rate Rise

Test specimens are clamped into a circular test head where they are exposed to water pressure that increases at a constant rate. In ISO 811, the pressure is raised until water droplets appear in three different places on the fabric surface. The pressure at which this occurs is recorded in millibar or millimetre water column.

Fabric Construction

Durable coatings and membranes are tested using this protocol to ensure they can withstand the pressure of heavy rain or kneeling on wet ground. For ISO 811, a higher hydrostatic head number represents a more effective water barrier, with premium outdoor garments often exceeding ten thousand millimetres. The rate of pressure rise can be adjusted depending on the fabric type, which makes it adaptable for both light and heavy textiles.

This adaptability allows mills to benchmark a wide range of barrier finishes.

Waterproof Claims

Sourcing contracts for outdoor and protective clothing rely on these test numbers to justify their performance claims. Failing ISO 811 can lead to garments leaking during use, which would damage the brand’s reputation for quality. It remains the essential laboratory test for waterproofing in the apparel industry.