Testing PU-Coated Waterproof Fabric: Hydrostatic Head, Breathability and Wash Durability

How PU-coated waterproof fabric is tested for waterproofness, breathability and durability: hydrostatic head, MVTR and RET, spray rating, seam leakage and wash cycling, with the figures buyers should ask for.

Hydrostatic head: the waterproofness number

Hydrostatic head measures how much water pressure the fabric withstands before leaking, expressed in millimetres of water column and usually tested to ISO 811 or AATCC 127.

For PU-coated waterproof fabric, the useful reading is the figure after ageing, flexing and washing rather than the figure on a fresh sample, because that is the number that predicts field complaints.

Breathability: MVTR and RET

Breathability is reported either as moisture vapour transmission rate in grams per square metre per day or as resistance to evaporative heat transfer, where a lower RET means a more breathable fabric.

The two are not interchangeable, so a specification for PU-coated waterproof fabric should name the method, and a sensible target reads roughly as 3,000-10,000 mm hydrostatic head with more limited breathability, at roughly 90-150 gsm.

Spray test and water repellency

The spray test rates how well the surface sheds water from zero to one hundred, and the rating after repeated laundering matters more than the initial result.

A fabric that still beads at eighty after twenty washes will keep a wearer comfortable far longer than one that starts at a hundred and wets out after three.

Seams and the finished garment

Fabric performance is worthless if the needle holes leak, so the rain tower and seam leakage tests belong in the approval of any garment built from PU-coated waterproof fabric.

Test finished garments rather than swatches at least once, because tape application, zip construction and pattern design decide whether a shell stays dry.

Wash durability and care testing

Wash cycling reveals delamination, DWR loss, shade change and dimensional movement, and five to twenty cycles is a realistic window for an outdoor shell.

Record the result of every cycle for PU-coated waterproof fabric, since gradual decline is normal and the pace of that decline is what a brand should be choosing between.

Summary

A clear specification, a retained reference sample and documented testing together remove most of the risk from buying PU-coated waterproof fabric for outdoor sportswear.