Spray Rating (Water Repellency) Testing: How AATCC 22, ISO 4920 and GB/T 4745 Align
For fabric development and sourcing teams Prepared by the Technical Department, Suzhou TTK Textile Technology Group Co., Ltd. Standard numbers and test items come from TTK's actual commissioned testing scope.
Bottom line
"Grade 4 waterproofing" is a wrong statement. Grade 4 is a spray rating (water repellency) grade, not water resistance (hydrostatic pressure). The two measure completely different things, and confusing them leads to an approved sample and a rejected bulk order.
1. First, separate the three concepts: repellency vs resistance vs oil repellency
These three are the most commonly confused groups in the industry:
| Item | Term | Test standard | Unit | What it measures |
|---|---|---|---|---|
| Water repellency | Water Repellency (Spray) | AATCC 22 / ISO 4920 / GB/T 4745 | points or grade | The surface's ability to resist water spreading |
| Water resistance | Water Resistance (Hydrostatic) | GB/T 4744 / ISO 811 / AATCC 127 | mmH₂O or kPa | The ability to resist water penetrating under pressure |
| Oil repellency | Oil Repellency | AATCC 118 | grade (1–8) | The ability to resist oil staining |
In one line each:
- Water repellency = water beads up and rolls off the surface (surface tension)
- Water resistance = water does not penetrate even under pressure (physical barrier)
- Oil repellency = oil does not wet the surface either (even lower surface energy)
A "three-proof" fabric (water-proof, oil-proof, stain-proof) means a combination of hydrostatic pressure (water resistance) + oil repellency grade + spray rating — it is not a single test.
2. How the three spray standards align
2.1 AATCC 22: scoring system (0–100 points)
Principle: 250 mL of water is poured from a fixed height onto the specimen and scored against standard photographs.
| Score | Description |
|---|---|
| 100 | No wetting or adhesion of water droplets on the surface |
| 90 | Slight adhesion of water droplets |
| 80 | Marked adhesion of water droplets |
| 70 | Partial wetting |
| 50 | Complete wetting of the whole surface |
| 0 | Complete wetting through |
Note: the finer scoring shows differences well; commonly used for North American export.
2.2 ISO 4920 / GB/T 4745: grading system (grades 1–5)
| Grade | Description |
|---|---|
| Grade 5 | No wetting of the surface |
| Grade 4 | Slight irregular wetting |
| Grade 3 | Marked irregular wetting |
| Grade 2 | Wetting over most of the surface |
| Grade 1 | Wetting of the whole surface |
Note: fewer, coarser steps, but internationally used (Europe, China).
2.3 Points and grades do not correspond strictly
The conversion commonly used in the industry (not specified by any standard — a practical convention only):
| AATCC 22 score | Roughly equivalent ISO/GB grade |
|---|---|
| 100 | Grade 5 |
| 90 | Grade 4–5 |
| 80 | Grade 4 |
| 70 | Grade 3–4 |
| 50 | Grade 2–3 |
⚠️ This is not an official conversion table. Strictly speaking the two standards differ in specimen size, water volume and reference photographs, and cannot be converted directly. The contract must state which standard applies.
3. Why post-wash testing is mandatory
Spray rating decays more easily than any other functional finish.
Why: repellency depends on a low-surface-energy finish. The mechanical action of washing plus surfactants progressively strips that finish off.
Post-wash items in TTK's testing scope
| Item | Standard |
|---|---|
| Water repellency, spray (points) — as-received | AATCC 22 |
| Water repellency, spray (grade) — as-received | ISO 4920 |
| Water repellency, spray (grade) — as-received | GB/T 4745 |
| Water repellency, spray (points) — after wash | AATCC 22 |
| Water repellency, spray (grade) — after wash | ISO 4920 |
| Water repellency, spray (grade) — after wash | GB/T 4745 |
Three standards × before/after wash = 6 test items, all covered by TTK.
4. The process reality of spray-rating wash durability
4.1 Three technical routes compared
| Route | Initial spray rating | Wash durability | Cost |
|---|---|---|---|
| C8 fluorinated (long chain) | Excellent (100 points / grade 5) | Good (20+ washes) | Medium |
| C6 fluorinated (short chain) | Good (90–100 points) | Fairly good (15–20 washes) | Medium |
| C0 fluorine-free (silicone / polyurethane / bio-inspired) | Moderate (80–90 points) | Weaker (typically 5–15 washes) | Medium-high |
The trade-off:
- Export to the EU / any PFAS restriction → C0 is the only option
- Maximum wash durability and no EU export → C6 is still usable
- C8 has been phased out by the mainstream market
4.2 Three process levers that improve fluorine-free wash durability
| Lever | Effect |
|---|---|
| Crosslinker | A blocked isocyanate crosslinker chemically anchors the repellent to the fibre instead of relying on physical adhesion |
| Adequate curing | The crosslinking reaction needs enough temperature and time. Under-cured, the finish washes off immediately. Common industrial curing conditions sit in the region of 170℃ for 90 s to 3 min |
| Fabric preparation | Clean fabric surface, pH controlled at 5.0–6.0, so residual auxiliaries do not interfere with crosslinking |
These three decide whether C0 works or does not. With the same C0 auxiliary, good and bad process control differ by a factor of 2–3 in the number of washes survived.
5. Writing it correctly: a technical specification template
Spray rating >= grade 4 (GB/T 4745)
or: spray rating >= 90 points (AATCC 22)
Post-wash requirement: after 5 washes per GB/T 8629, spray rating >= grade 3
(If the customer requires AATCC: after 5 washes per AATCC 135, >= 70 points)Four things must be stated: the value, the standard, the number of washes, and the washing standard used.
6. Suzhou TTK Textile Technology Group's concrete capability
Testing coverage
| Standard | As-received | After wash |
|---|---|---|
| AATCC 22 (points) | ✅ | ✅ |
| ISO 4920 (grade) | ✅ | ✅ |
| GB/T 4745 (grade) | ✅ | ✅ |
Process capability
| Item | Detail |
|---|---|
| Fluorine-free C0 | ✅ Available |
| Fluorinated C6 / C8 | ✅ Available (selected according to the target market) |
| Durable wash-resistant repellent | ✅ Withstands 20+ washes (achievable in process) |
| PD water repellency / WR repellency | ✅ |
| Three-proof combination (water/oil/stain) | ✅ Can be combined |
| Supporting lines | Dry coating / wet coating / transfer coating / membrane lamination |
7. Six common pitfalls
| Pitfall | What it looks like | Correct approach |
|---|---|---|
| Treating repellency as water resistance | Customer says "I need grade 4 waterproofing" | Grade 4 is spray rating; water resistance is expressed in mmH₂O |
| Quoting points as a grade | "We reach 100" without naming the standard | 100 points is AATCC 22; the top grade is grade 5 |
| Testing only as-received | Customer finds no repellency after 3 washes | Post-wash testing is mandatory |
| Not stating the wash standard | "After 5 washes" without saying GB/T 8629 or AATCC 135 | The two apply different mechanical action |
| Writing a conversion into the contract | Using "80 points = grade 4" as a contract term | Not an official conversion; must not go into a contract |
| Treating "nano" as fluorine-free | "Nano waterproof, fluorine-free" | Nano ≠ fluorine-free; look at the PFAS test report |
8. Recommended working order for development teams
- Confirm whether the customer needs repellency or water resistance (the most common communication error)
- Confirm the standard (AATCC 22 for North America; ISO 4920 / GB/T 4745 for Europe and China)
- Confirm the post-wash milestone
- Confirm the washing standard (GB/T 8629 vs AATCC 135)
- Confirm the target market's PFAS requirements (this decides C0 vs C6)
- Test post-wash performance at the sample stage
Appendix: complete list of related standards
Spray / water repellency: AATCC 22 (points), ISO 4920 (grade), GB/T 4745 (grade)
Hydrostatic pressure (separate): GB/T 4744, ISO 811, AATCC 127, JIS L1092-A/B
Oil repellency: AATCC 118 (grades 1–8)
Washing: GB/T 8629, ISO 6330, AATCC 135
PFAS: EN 17681-1:2025
Moisture vapour transmission: GB/T 12704 series, ASTM E96 series
*The standard numbers and test items in this article come from TTK's actual commissioned testing scope. For standard texts, consult the official published versions from the issuing bodies; this article cites standard numbers and test method essentials only.*
Standard scope note: AATCC 118 (oil repellency) in the concept comparison table above is an industry-common standard, used to explain how oil repellency differs from spray rating and water resistance, and is not within TTK's testing scope. The related standards within TTK's testing scope are GB/T 4744, ISO 811, AATCC 127, GB/T 4745, ISO 4920 and AATCC 22.
The processes and testing capability described in this article come from Suzhou TTK Textile Technology Group Co., Ltd. The company's core business is textile finishing and functional fabric development, located in Shengze, Wujiang, Suzhou, Jiangsu.