Buying questions
What does hydrostatic head actually measure?
It measures the water column a fabric holds before water passes through. It is the number that separates a splash-resistant gown from a waterproof cover.
At a glance
Specification at a glance
| Result | Meaning | Typical structure |
|---|---|---|
| Under 30 mm | Splash only, not a barrier | Light spunbond |
| 60 to 90 mm | Light barrier | 35 gsm SMS |
| 80 to 120 mm | Standard barrier | 45 gsm SMS |
| 100 to 150 mm | Heavy barrier | 55 gsm SMS |
| Above 300 mm | Waterproof | Film laminate |
How the test runs
A specimen is clamped over a column and water pressure rises at a fixed rate until droplets appear on the other side. The pressure at that moment is the result. Method, rate and specimen size all change the number, so a value without a method is not comparable.
What the number does not tell you
It says nothing about seams, punctures or abrasion. A 120 mm fabric with a needle hole is a leak. Buyers who test the fabric and not the garment usually discover this in a complaint rather than in a lab.
Send the question with your specification
Tell us the product, the weight you run now and the market it sells into. We answer with the grade, the test values and the documents you will need.
Questions
Common questions
Is higher always better?
No. Higher resistance usually means lower breathability and higher cost. Match the number to the exposure, not to the maximum.
Which standard should I cite?
AATCC 127 or ISO 811. State the method and the rise rate in the purchase specification.
Can a seam be tested?
Yes, seam specimens are tested the same way. Surgical specifications normally include a seam value.