Moisture Vapour Transmission Testing: GB/T 12704, ASTM E96 and JIS L1099 Compared
For fabric development, sourcing and laboratory liaison 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
An MVTR figure has no absolute value — only "the value measured by a given standard". For the same fabric, GB/T 12704.1 and ASTM E96-BW can differ by more than a factor of two. A contract that does not state the method has handed itself a reason for rejection.
1. First, separate three concepts
Most disputes come from these three terms being used interchangeably:
| Concept | Term | Unit | What it measures |
|---|---|---|---|
| Moisture vapour transmission rate | MVTR | g/m²/24h | The total amount of water vapour passing through the fabric |
| Water vapour permeability | Water Vapor Permeability | g·mm/m²·24h | The material's own transmission ability, with thickness factored out |
| Air permeability | Air Permeability | L/(m²·s) or mm/s | The amount of air passing through — unrelated to moisture vapour |
The most common error: the customer says "breathable" when what they mean is "moisture vapour permeable". These are completely different tests.
A completely air-impermeable hardshell can have excellent MVTR; a highly air-permeable mesh can be completely non-water-resistant. Confirm which one is being asked for.
2. The 7 MVTR standards covered by TTK's testing scope
These are the moisture vapour transmission standards in TTK's actual commissioned testing scope:
2.1 Chinese national standards (GB/T 12704 series)
| Standard | Method name | Principle | Suited to |
|---|---|---|---|
| GB/T 12704.1 | Desiccant method | Desiccant inside the cup; the absorbed water is weighed | Standard fabrics; stable results |
| GB/T 12704.2-A | Evaporation method A | Water inside the cup; the loss in weight is measured | High-MVTR fabrics |
| GB/T 12704.2-B | Evaporation method B | As above, different test conditions | As above |
Key point: 12704.1 and 12704.2 work in opposite directions (one absorbs, one evaporates), so their results cannot be compared directly.
2.2 US standards (ASTM E96 series)
| Standard | Method code | Meaning |
|---|---|---|
| ASTM E96-B | Method B | Desiccant method |
| ASTM E96-BW | Method BW | Desiccant method, wet cup |
| ASTM E96-E | Method E | Water method |
The difference between BW and E: whether the cup holds a desiccant or water directly changes the driving force, so the results differ.
2.3 Japanese standard
| Standard | Note |
|---|---|
| JIS L1099-B1 | Japanese MVTR test method; common on Japanese orders |
3. Why the results differ so much: the driving-force principle
Moisture vapour transmission is essentially diffusion driven by a water vapour partial pressure difference.
MVTR ∝ water vapour partial pressure difference × permeability coefficient ÷ thicknessThat single relationship explains all the variation:
| Variable | Effect |
|---|---|
| Water or desiccant in the cup | Water provides a near-saturated vapour pressure, a large driving force → high figure; a desiccant provides a near-zero vapour pressure, a small driving force → low figure |
| Test temperature and humidity | Saturated vapour pressure roughly doubles for every 10℃ rise |
| Air velocity | Airflow across the cup mouth changes the boundary layer thickness |
| Specimen thickness | Thick fabric gives a lower MVTR (same material) |
So the statement "MVTR 5,000" means nothing on its own. You must ask: by which standard, at what temperature and humidity, on how many specimens.
4. Writing it correctly: a technical specification template
MVTR >= 5,000 g/m²/24h
Test method: GB/T 12704.1 (desiccant method)
Test conditions: 38±2℃, 50±5% relative humidity
Specimens: 3, average taken
Post-wash requirement: after 5 washes per GB/T 8629, MVTR >= 4,000 g/m²/24hSix items, none optional: the value, the standard, the temperature and humidity, the number of specimens, how the value is derived, and the post-wash requirement.
5. Four technical routes to a moisture-permeable functional fabric
Moisture permeability does not have to mean a laminated membrane. TTK's process capability covers four routes:
| Route | Principle | MVTR | Water resistance | Hand feel |
|---|---|---|---|---|
| Hydrophilic non-porous | Molecular chain segments transmit vapour; no physical pores | Moderate | Good (no pores means no channels) | Soft |
| Microporous | Wet-process PU foaming creates micropores, smaller than water droplets but larger than vapour molecules | High | Good (vapour passes, water does not) | Fairly stiff |
| Single-component permeable | The single coating layer is itself permeable; no laminated membrane needed | Moderate to low | Moderate | Lightest |
| Two-component permeable | Two functional layers working together | High | Good | Moderate |
Key process parameters for the microporous route
Microporous coating (wet-process PU foaming) is fundamentally about controlling pore size:
- Solids content: affects the dry film thickness and pore regularity
- Coagulation bath composition: the DMF-to-water ratio determines the phase separation rate
- Coagulation bath temperature: higher temperature means faster phase separation, larger and less regular pores; lower temperature gives finer, denser pores
- Coating thickness: thicker gives lower MVTR but higher hydrostatic pressure
The essence of this line is trading microstructure for performance: pores small enough to hold water back, numerous enough to let vapour through. The process window is narrow — parameters off by a little and you either lose MVTR or lose hydrostatic pressure.
6. Moisture permeability and hydrostatic pressure: a built-in conflict
| Goal | Process tendency | Cost |
|---|---|---|
| Higher hydrostatic pressure | Thicker coating, denser film | Lower MVTR |
| Higher MVTR | Thinner coating, more pores | Lower hydrostatic pressure |
There is no solution that maximises both. A brand has to make a trade-off when setting targets, and where that point falls depends on the use case:
| Use case | Hydrostatic pressure | MVTR | Trade-off tendency |
|---|---|---|---|
| Urban hardshell | Moderate (5,000–10,000 mmH₂O) | Moderate | Balanced |
| Technical mountaineering | High (15,000+) | Moderate-high | Favours hydrostatic pressure |
| High-intensity sport (trail running) | Moderate | High | Favours MVTR |
| Raincoat / rain cover | Very high | Low | MVTR not considered |
7. Suzhou TTK Textile Technology Group's concrete capability here
Testing coverage
| Standard | Test item available |
|---|---|
| GB/T 12704.1 (desiccant method) | ✅ |
| GB/T 12704.2-A (evaporation method A) | ✅ |
| GB/T 12704.2-B (evaporation method B) | ✅ |
| ASTM E96-B | ✅ |
| ASTM E96-BW | ✅ |
| ASTM E96-E | ✅ |
| JIS L1099-B1 | ✅ |
Post-wash MVTR items are covered as well (for comparison against the as-received state).
Test report inventory
Suzhou TTK Textile Technology Group holds 591 unique test reports on outdoor functional fabrics (issued by FCL), after de-duplication, of which 62 cover moisture vapour transmission.
Process capability
All four permeable routes run on the company's own lines:
| Route | Process implementation |
|---|---|
| Hydrophilic non-porous | Hydrophilic PU coating; dry, wet and transfer processes all available |
| Microporous | Wet-process PU foaming; own wet coating line plus small-batch wet coating line |
| Single-component permeable | Direct single-layer coating |
| Two-component permeable | Two-coat combination |
Supporting lamination capability: TPU / PU / PTFE / PE membrane lamination, 2L / 2.5L / 3L constructions, and dot, flame and PUR hot-melt lamination.
8. Six common pitfalls
| Pitfall | What it looks like | Correct approach |
|---|---|---|
| No standard quoted | Just "MVTR 5000" | State the standard plus temperature and humidity |
| Air permeability taken as MVTR | Customer asks for "breathability" and air permeability is tested | Confirm first whether MVTR or air permeability is wanted |
| Comparing 12704.1 with .2 | Desiccant-method data compared against evaporation-method data | The two work in opposite directions; not comparable |
| No post-wash data | As-received data only | Garments are washed; post-wash testing is required |
| No specimen count or averaging rule | A single figure | State 3-specimen average or minimum value |
| Wrong unit | g/m²/24h and g·mm/m²·24h used interchangeably | The latter includes thickness; the numbers are entirely different |
9. Recommended working order for development teams
- Confirm first whether it is MVTR or air permeability
- Confirm the standard (what the export customer uses, what domestic customers use)
- Confirm the temperature and humidity conditions (they may differ between laboratories)
- Confirm the post-wash requirement (how many washes, by which washing standard)
- Test post-wash performance at the sample stage, not after bulk production
- Keep the full test conditions in the technical file
Appendix: complete list of related standards
Moisture vapour transmission: GB/T 12704.1, GB/T 12704.2-A, GB/T 12704.2-B, ASTM E96-B, ASTM E96-BW, ASTM E96-E, JIS L1099-B1
Air permeability (tested separately): GB/T 5453, ISO 9237
Hydrostatic pressure: GB/T 4744, ISO 811, AATCC 127, JIS L1092-A/B
Spray / water repellency: AATCC 22, ISO 4920, GB/T 4745
Washing (for post-wash testing): GB/T 8629, ISO 6330, AATCC 135
*The standard numbers and test items in this article come from TTK's actual commissioned testing scope; report data come from FCL test reports. 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.