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In spec sheets the two words are used loosely, but they answer different questions. Water repellency (often called water-resistance) is about the surface: does a droplet bead up and roll off, or soak in? Waterproofness is about pressure: can the cloth stop liquid water that is being pushed through it, the way rain is pushed against a shoulder or a knee against wet ground? Two different tests measure the two, and a good number on one does not guarantee the other.
This is the surface-repellency test. A specimen is mounted flat on a ~150 mm (6 in) hoop, tilted 45°, and 250 ml of distilled water at 27°C is sprayed from a standard nozzle 150 mm above it over 25–30 seconds. The wetting pattern is compared against a photographic chart.
| AATCC 22 score | ISO 4920 grade | What you see |
|---|---|---|
| 100 | 5 | No wetting — full beading |
| 90 | 4 | Slight random wetting; high-performance rainwear target |
| 80 | 3 | Wetting at the spray points; "standard" performance |
| 70 | 2 | Partial wetting of the whole upper face |
| 50 | 1 | Complete wetting of the upper face |
| 0 | 0 | Soaked through both sides |
The score reflects the DWR (durable water-repellent) finish on the surface — not a membrane or coating underneath. Outdoor rainwear is usually specified at 90+ (ISO 4) before washing and 80+ (ISO 3) after the agreed wash cycles.
This is the pressure test. The specimen is clamped and water is pushed against it from below, with the pressure rising at a controlled, constant rate. The result is the height of the water column — in millimetres of water (mm H₂O) — at which droplets begin to appear on the upper face. (ISO 811 records at the third droplet to rule out stray beads.)
For context: 1,000 mm H₂O ≈ 9.8 kPa, and 10,000 mm ≈ 98 kPa, close to 1 bar. The standard itself sets no pass/fail threshold — the "waterproof" lines below are industry convention, not the method.
| Hydrostatic head (mm H₂O) | Common reading | Typical use |
|---|---|---|
| below ~1,000 | water-repellent only | light showers, sheds droplets |
| 1,000–1,500 | highly water-resistant | everyday light rain |
| 1,500–5,000 | waterproof, light duty | commuter / fashion rainwear |
| 5,000–10,000 | waterproof, medium duty | outdoor, tents, awnings |
| 10,000+ | technical / heavy duty | alpine, sustained rain |
Sitting on wet ground is roughly 1,500–2,000 mm of pressure; kneeling is closer to 10,000 mm. Above about 3,000 mm the fabric already exceeds the pressure of a one-metre immersion, so extra height mostly pays for abrasion, flexing and ageing — and ratings above ~20,000 mm are often more marketing than need.
See also our breathability guide — a waterproof finish reduces vapour escape, so balance repellency against comfort — and the tensile & tear guide, because abrasion drops the hydrostatic head over a garment's life.
We are an integrated woven mill — yarn dyeing, weaving, fabric dyeing, printing and finishing on one site — so water-repellent (DWR) finishing is applied in-house as part of the same flow. The exact achievable spray rating, and any hydrostatic head for coated or laminated constructions, is confirmed per order in writing (available on request). Tell us your end use and target rating on the quote request and we will specify a route that meets it.
No. Once a fabric passes roughly 3,000 mm H2O it already exceeds the pressure of a one-metre immersion, so higher numbers mainly buy resistance to abrasion, flexing and ageing. Ratings above about 20,000 mm are often more about marketing than real need — and a higher barrier usually costs breathability.
They measure the same physical effect with the same apparatus, just on different scales: AATCC 22 scores 0–100, ISO 4920 grades 1–5, and they map directly (100=5, 90=4, 80=3, 70=2, 50=1, 0=0). Always compare like for like and the same method across labs.
Not necessarily. The spray test scores the surface DWR finish; the hydrostatic head test scores penetration under pressure. A cloth can bead water on the surface yet soak through when rain is pushed against it, so a rain garment needs both numbers.
No. It tests flat, clamped fabric only. Real leaks start at seams, zips and welds, which is why garment waterproofing also depends on seam taping or welding — a separate construction step from the cloth rating.