UV Protection (UPF) Testing: How EN 13758-1, AATCC 183 and GB/T 18830 Differ, and Why Post-Wash Matters
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
UPF 50+ does not mean "still UPF 50+ after washing". UV protection decays more noticeably than any other functional finish, so as-received data alone says nothing. The three mainstream standards also judge differently and cannot be converted into one another.
1. Three standards, three test approaches
| Standard | Origin | Method essentials | Result reported as |
|---|---|---|---|
| GB/T 18830 | Chinese national standard | Measures transmittance in the UVA and UVB bands and calculates UPF | UPF value + UVA transmittance |
| EN 13758-1 | European standard | Spectrophotometric measurement of transmittance over 290–400 nm | UPF value + grading marking |
| AATCC 183 | US standard | Measures UV transmittance and calculates UPF | UPF value |
1.1 The key difference: the thresholds for a claim
| Claim | GB/T 18830 | EN 13758-1 | AATCC 183 |
|---|---|---|---|
| UPF 50+ | UPF > 40 and UVA transmittance < 5% | UPF > 40 and UVA transmittance < 5% | UPF ≥ 50 (in some editions) |
| May be called a "UV-protective product" | UPF > 40 and UVA < 5% | UPF > 40 and UVA < 5% | — |
Note: the Chinese and European standards set essentially the same conditions for "UPF 50+" (UPF > 40 and UVA < 5%), while the US standard sets a higher threshold for UPF 50+.
So the same fabric may be labelled UPF 50+ under GB/T 18830 but only UPF 40+ under AATCC 183.
1.2 UVA transmittance is the condition people forget
Most people watch the UPF value and forget UVA transmittance.
Both the Chinese and the European standard require: labelling UPF 50+ needs UPF > 40 and UVA transmittance < 5% at the same time.
Two fabrics may both have UPF 60, but one has UVA transmittance of 3% and the other 7%. The latter cannot be labelled UPF 50+, because the UVA condition fails.
2. Why post-wash testing is mandatory
2.1 Why UV protection decays
UV-protective finishing works in one of two ways:
- Absorption: UV absorbers (organic or inorganic) take up UV energy
- Reflection / shielding: inorganic particles such as titanium dioxide and zinc oxide reflect and scatter
Decay mechanisms:
- Absorbing auxiliaries are progressively washed out → UPF drops noticeably
- Inorganic particles adhere through a binder; as the binder ages the particles come off → UPF drops
- Fabric stretched or abraded opens up the pores → transmittance increases
The result: UV protection is among the fastest-decaying of all functional finishes; after 10 washes UPF can fall by more than half.
2.2 What TTK's testing scope covers
| Item | Status |
|---|---|
| UV protection (as-received) | ✅ Available |
| Spectral reflectance | ✅ Available (used to assess the effect of reflective finishes) |
Note: some reflective / reflective-type functional fabrics need the spectral reflectance curve, not just a single UPF number.
3. Four fabric factors that drive UPF
3.1 Fabric structure (a bigger influence than the finish)
| Factor | Effect |
|---|---|
| Cover factor / tightness | The smaller the pores, the harder for UV to pass. This is the most fundamental factor |
| Mass per unit area | For the same structure, thicker means higher UPF |
| Yarn fineness | Fine yarns, densely woven, give high UPF |
| Colour | Dark colours absorb UV better than light ones (the same fabric dyed darker has a higher UPF) |
The key insight: a finish can raise UPF, but the base fabric structure sets the ceiling. On a sparse, thin fabric, no finish will deliver UPF 50+ with wash durability.
3.2 The effect of colour on UPF
For the same fabric in different colours, UPF can differ by more than 30%:
| Colour | Relative UPF |
|---|---|
| Dark (black, navy, deep red) | High |
| Medium | Medium |
| Light (white, ecru, pale pink) | Low |
This explains a common problem: the customer approves a sample tested in ecru at UPF 50+, then the bulk order in pale blue fails. Test against the lightest colour.
3.3 Stretched and wet states
| State | Change in UPF |
|---|---|
| Dry | Baseline |
| Wet | UPF drops (water fills the pores, but UV can pass through water) |
| Stretched 10% | UPF drops noticeably (pores open up) |
Demanding customers will ask for wet and stretched-state testing. The test state should be stated in the technical specification.
4. Writing it correctly: a technical specification template
UV protection: UPF > 40, UVA transmittance < 5% (GB/T 18830)
(or per EN 13758-1 / AATCC 183 — state which)
Test state: dry
Colour: test one set each in the darkest and lightest colour of the batch
Post-wash requirement: after 10 washes per GB/T 8629, UPF still > 40
Specimens: 4 per colour, average taken (required by some standards)Six items, none optional: the value, the standard, the test state, the colour selection, the post-wash requirement, and the specimen count and averaging rule.
5. Suzhou TTK Textile Technology Group's concrete capability
Testing coverage
| Standard | Status |
|---|---|
| GB/T 18830 | ✅ |
| EN 13758-1 | ✅ |
| AATCC 183 | ✅ |
| Spectral reflectance | ✅ |
Process capability
UV protection can be achieved by the following processes, all on the company's own lines:
| Process | Detail |
|---|---|
| UV-protective coating | UV absorbers or shielding particles added to the coating |
| Functional finishing (pad-dry-cure) | UV-protective finishing agent applied by padding and curing |
| Combination with lamination | Combined with waterproof-breathable laminated constructions |
Can be combined with other functions:
- UV protection + water resistance (hydrostatic pressure)
- UV protection + moisture management
- UV protection + cooling sensation (note the compatibility of the two finishes)
Test report inventory
Suzhou TTK Textile Technology Group holds 591 unique test reports on outdoor functional fabrics (issued by FCL), after de-duplication. The UV-related items are covered within the testing scope.
6. Compatibility when combined with other functions
6.1 UV protection + cooling sensation
They interfere with each other: a cooling sensation depends on instant heat conduction at the moment of contact, and a UV-protective coating can change the surface feel.
Approach: when the two finishes are combined in one process, the cooling value (Qmax) requires separate third-party testing to confirm — it cannot be assumed that two separately tested finishes simply add up.
6.2 UV protection + water resistance
Usually compatible: UV absorbers can be incorporated into a water-resistant coating system.
But note: thickening the coating to raise hydrostatic pressure may change the surface structure enough to affect the UPF measurement.
6.3 UV protection + flame retardancy
Handle with care: some flame-retardant systems chemically interfere with UV-protective auxiliaries.
7. Six common pitfalls
| Pitfall | What it looks like | Correct approach |
|---|---|---|
| Testing only as-received | UPF collapses after washing | Post-wash testing is mandatory |
| Looking at UPF but not UVA | UPF 60 but UVA 7% | GB/T 18830 and EN 13758-1 require UVA < 5% |
| Mixing standards | Labelled UPF 50+ under GB/T 18830, retested by the customer under AATCC 183 and failing | Test to the target market's standard |
| Testing the sample colour only | Ecru passes, bulk pale blue fails | Test the lightest colour |
| Testing dry state only | Customer requires wet state | State the test state in the technical specification |
| Treating UPF as SPF | Confusing a fabric metric with a cosmetic metric | UPF is for fabric, SPF is for cosmetics |
8. Recommended working order for development teams
- Confirm the target market's standard (GB/T 18830 in China, EN 13758-1 in Europe, AATCC 183 in North America)
- Confirm both UPF and UVA
- Confirm the post-wash milestone
- Sample and test against the lightest colour
- Confirm the test state (dry/wet, stretched or not)
- Confirm compatibility retesting when combining with other functions
Appendix: complete list of related standards
UV protection: GB/T 18830, EN 13758-1, AATCC 183
Washing (for post-wash testing): GB/T 8629, ISO 6330, AATCC 135
Related physical properties: GB/T 5453 / ISO 9237 (air permeability), GB/T 12704 series (moisture vapour transmission), GB/T 4744 series (hydrostatic pressure)
Colour fastness: GB/T 3920 / ISO 105 X12 (rubbing), GB/T 3921 / ISO 105 C06 (soaping)
*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.*
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.