Determination of Water Vapor Transmission of Hardshell Jackets: Test Methods, Standards, and Result

Water vapor transmission (WVT) testing is the core method for quantifying the breathability of hardshell jackets, verifying whether waterproof-breathable membranes and coatings can effectively transport body moisture to the outside environment. This technical article explains the measurement principle of WVT determination, the relevant GB, ISO, EN, ASTM, and JIS standards, specimen preparation, gravimetric dish methods, sweating hot plate procedures, and how to correctly interpret WVTR and Ret results for quality control and product certification.

Technical Overview

A hardshell jacket is a windproof, rainproof outdoor shell garment constructed with a waterproof-breathable barrier, typically an expanded PTFE or polyurethane-type membrane, or a hydrophilic coating, laminated or coated onto a face fabric. These garments must satisfy two inherently conflicting requirements: blocking external liquid water (rain, sleet, wet snow) while allowing water vapor generated by body perspiration to escape. Determination of water vapor transmission (WVT) quantifies the second requirement and is one of the most important indicators of wearing comfort.

WVT performance can be expressed in two complementary ways: as a water vapor transmission rate (WVTR) in g/(m²·24 h), measured gravimetrically or with rapid sensors, or as water vapor resistance (Ret) in m²·Pa/W, measured with a sweating guarded-hot plate. Both approaches establish a controlled water vapor pressure gradient across the specimen and quantify the resulting vapor flow. Results are strongly method-dependent, so the test method and its conditions must always accompany any reported value.

• WVTR — the mass of water vapor passing through a unit area of fabric per 24 hours, g/(m²·24 h); higher values indicate better breathability.
• Ret — water vapor resistance of a textile ensemble under steady-state conditions, m²·Pa/W; lower values indicate better breathability.
• Related properties — waterproofness (hydrostatic pressure), surface spray rating, and seam integrity are evaluated alongside WVT to characterize the complete waterproof-breathable system.

Testing Samples

Fabric-Level Specimens

Specimens are cut from roll fabric or from representative panels of the finished garment (chest, back, and sleeve locations are typical), avoiding seams, taped areas, prints, and damaged regions. A minimum of three replicate specimens per test condition is customary, and five is preferred for statistical reliability. Specimen size is governed by the dish or plate aperture, typically around 50 mm to 100 mm in diameter or square. All specimens are conditioned before testing in a standard textile atmosphere of 20 ± 2 °C and 65 ± 4 % relative humidity for a defined period (commonly 24 hours), in accordance with GB/T 6529 or ISO 139.

Garment-Level Specimens

Because finished garments incorporate seam tape, zippers, linings, and ventilation features, fabric-level results do not always reflect whole-garment performance. For full-system evaluation, entire jackets can be tested on a sweating thermal manikin, or multiple panels can be cut from the garment and tested individually to map position-dependent breathability.

Aged and Treated Specimens

To assess durability, WVT is frequently re-measured after pre-treatment, for example after repeated laundering cycles in accordance with GB/T 8629 or ISO 6330, after abrasion or flexing, or after artificial aging. A decline in WVTR after washing may indicate membrane contamination, delamination, or damage to the breathable layer.

Testing Items

Typical test items within a water vapor transmission program for hardshell jackets include:

• Water vapor transmission rate (WVTR) by the upright desiccant method, upright evaporative (water) method, or inverted cup method.
• Water vapor resistance (Ret) using the sweating guarded-hot plate (skin model).
• Retention of breathability after laundering, abrasion, or flexing.
• Complementary waterproofness verification, such as hydrostatic pressure resistance and surface water repellency (spray rating), to confirm that breathability improvements have not compromised the water barrier.
• Comparison testing of different membrane or coating constructions under identical conditions for material selection.

Testing Methods

Upright Evaporative Dish Method (Water Method)

This gravimetric procedure follows GB/T 12704.2 and corresponds conceptually to the water methods of ASTM E96/E96M and the gravimetric approach of ISO 2528. A test dish is partially filled with water, leaving a defined air gap between the water surface and the specimen. The fabric is sealed over the dish mouth, usually with molten wax or a gasket, ensuring that vapor can escape only through the specimen. The assembly is placed in a climatic chamber under strictly controlled temperature and relative humidity — typically 38 °C with low-to-moderate chamber humidity for the evaporative method — and weighed at defined intervals. The mass loss of the assembly, caused by water vapor diffusing through the fabric, is used to calculate WVTR. The specimen orientation (body side toward the water) should reflect end use and must be reported.

Upright Desiccant Method

Described in GB/T 12704.1, ASTM E96/E96M (desiccant procedure), and JIS L 1099 (upright calcium chloride procedure), this method places freshly regenerated anhydrous calcium chloride desiccant inside the dish instead of water. The desiccant maintains near-zero humidity on the inner side while the chamber supplies a humid environment — commonly 38 °C with high relative humidity on the order of 90 % — driving vapor inward through the fabric. The mass gain of the desiccant assembly over time is measured and converted to WVTR. Exact parameter values must always be taken from the current edition of the applicable standard.

Inverted Cup Methods

Inverted cup configurations, such as ASTM E96/E96M Method BW and the potassium acetate inverted cup procedure of JIS L 1099, place the liquid or saturated salt solution in direct or near-direct contact with the specimen with the dish inverted. Because the vapor path through the fabric is shortened and the driving gradient is larger, inverted cup methods yield substantially higher numeric WVTR values than upright methods — often several times higher. These procedures are widely used in the outdoor apparel industry for high-performance membranes and marketing claims, but the results must never be compared directly with upright-method data.

Sweating Guarded-Hot Plate (Skin Model)

The sweating guarded-hot plate method, standardized in ISO 11092, EN 31092, and ASTM F1868, measures water vapor resistance (Ret) rather than a transmission rate. A porous sintered metal plate maintained at skin temperature (typically 35 °C) is supplied with controlled water to simulate perspiration. The specimen is placed above the plate, the surrounding guard ring and lower heating system eliminate lateral and downward heat losses, and the electrical power required to maintain steady-state evaporation is recorded. Ret is calculated from the difference between the saturation vapor pressure at the plate surface and the ambient vapor pressure, the plate area, and the evaporative heat flux. Ret reflects realistic physiological gradients and forms the basis of classification in European protective clothing standards; under EN 343 for rain protective clothing, water vapor resistance is graded in classes, with the best class corresponding to Ret values of approximately 20 m²·Pa/W or below.

Rapid Instrumental Methods

For production quality control of membrane films and laminates, sensor-based instruments dramatically shorten test times. ASTM F1249 employs a modulated infrared sensor to detect water vapor transmitted across the specimen into a dry carrier gas stream, while ASTM F2298 uses a dynamic moisture permeation cell to determine diffusion resistance under controlled, adjustable humidity gradients on each side of the fabric. These methods are precise, repeatable, and suited to high-throughput screening, though their results correlate only approximately with traditional dish methods.

Whole-Garment Sweating Manikin

For clothing-system-level evaluation, ASTM F2370 and the relevant clauses of ISO 9920 describe the determination of evaporative resistance using a sweating thermal manikin. A complete hardshell jacket is dressed on the manikin under standardized environmental conditions, capturing the combined effects of fabric breathability, seam taping, zipper construction, ventilation openings, fit, and inter-layer air gaps. This is the most realistic assessment of wearer comfort, and it typically shows higher total resistance than fabric-level data alone.

Calculation and Reporting

For gravimetric methods, the water vapor transmission rate is calculated as WVTR = (Δm × 24) / (A × t), where Δm is the change in assembly mass in grams, A is the effective test area in square meters, and t is the elapsed time in hours; the result is expressed in g/(m²·24 h). For hot plate testing, Ret = A × (ps − pa) / Qe, where ps and pa are the saturation vapor pressure at the plate surface and the ambient vapor pressure in pascals, A is the plate area, and Qe is the evaporative heat flow. A compliant test report must state the standard and method used, specimen orientation, test conditions (temperature, humidity, air velocity), individual and mean results, and any pre-treatment applied.

Result Interpretation and Typical Values

Because WVTR is an artifact of the test configuration, values only have meaning within a given method. As broad industry references under upright dish methods, coated fabrics commonly fall in the range of roughly 1,000 to 5,000 g/(m²·24 h), while high-performance membrane laminates frequently exceed 5,000 to 10,000 g/(m²·24 h); inverted cup procedures can report values several times higher for identical materials. For Ret, values below about 6 m²·Pa/W are generally regarded as very breathable, and values rising above 20 to 30 m²·Pa/W indicate noticeably reduced vapor transfer. In China, GB/T 32614 (Outdoor sportswear — Hardshell garments) assigns water vapor permeability results to graded performance classes used for product marking, and purchasers should verify claimed grades against the current standard edition. Interlaboratory variation of ±10 % to ±15 % is common for dish methods, so acceptance criteria should incorporate appropriate tolerances.

Factors Affecting Test Results

• Temperature and humidity gradient — higher temperature and larger vapor pressure differences increase measured WVTR.
• Test method and cup orientation — upright, inverted, hot plate, and sensor methods produce systematically different numbers for the same fabric.
• Air gap and air velocity — the distance between water surface and fabric, and chamber air movement, influence the boundary layer resistance.
• Specimen orientation and sealing — which fabric side faces the humid side matters for asymmetric laminates; poor edge sealing causes falsely high results.
• Fabric state — moisture content, prior laundering, DWR condition, membrane contamination, and physical damage all alter vapor transfer.
• Multi-layer effects — face fabric, membrane, scrim, and lining act in series; wetting-out of the face fabric after DWR loss can suppress overall breathability.

Applications

• New product development — comparing membrane, coating, and construction options during material selection for hardshell programs.
• Quality control — verifying incoming fabric lots and monitoring production consistency against internal WVTR or Ret specifications.
• Standards compliance — supporting classification and marking under GB/T 32614, EN 343, and related performance standards through accredited third-party laboratories.
• Marketing claim substantiation — validating advertised breathability figures such as "10,000 g" or "20,000 g" ratings with a traceable method reference.
• Durability assessment — quantifying breathability retention after washing, abrasion, flexing, and long-term use.
• Comfort research — supplying Ret inputs for physiological modeling, layering system design, and end-use recommendation.
• Dispute resolution and failure analysis — providing objective evidence when breathability complaints or delamination issues arise.

FAQ

Which standard should be used for hardshell jacket WVT testing?

For products sold in China, the GB/T 12704 series (desiccant and evaporative water methods) supports compliance with GB/T 32614 for hardshell garments. For European protective clothing applications, ISO 11092 / EN 31092 hot plate testing underpins EN 343 classification. For supplier data sheets and international comparison, ASTM E96/E96M, ASTM F1249, ASTM F1868, ASTM F2298, and JIS L 1099 are all widely accepted. The method should be chosen according to the target market, the certification scheme, and the end-use claim.

Why do WVTR results differ so much between test methods?

Each method creates a different vapor pressure gradient, air gap, and vapor path. Inverted cup methods place liquid directly against the membrane and therefore produce the highest values, while upright methods include a still air layer that adds resistance, and hot plate methods simulate a sweating skin at 35 °C. Values are only comparable when the method, orientation, and environmental conditions are identical.

What WVTR value counts as "good" for a hardshell jacket?

There is no universal pass line because the number depends on the method. As an industry rule of thumb under upright dish conditions, coated garments around 2,000 to 5,000 g/(m²·24 h) suit light activity, while serious mountaineering shells typically target well above 10,000 g/(m²·24 h) or, in hot plate terms, Ret below roughly 10 m²·Pa/W.

Can a finished jacket be tested, or only fabric?

Both. Panels can be cut from a finished jacket and tested by dish or hot plate methods, while a complete garment can be evaluated on a sweating thermal manikin per ASTM F2370, which also captures the effects of seams, zippers, and design features.

Does washing affect water vapor transmission?

It can. Detergent residues and dirt can block microporous membranes or plasticize hydrophilic layers, and loss of the durable water repellent finish causes the face fabric to wet out, which severely slows vapor transfer. Re-testing after standardized laundering is therefore a standard durability practice.

Are breathability and waterproofness related?

They are independent properties measured by different tests — WVTR or Ret for vapor transfer versus hydrostatic pressure testing for liquid water resistance. A fabric can be waterproof but not breathable (e.g., a simple PU coating), and certified hardshell garments must demonstrate both, typically together with seam-taping verification.

How many specimens and how long does testing take?

Dish methods normally require at least three to five specimens per condition, plus conditioning time; typical turnaround after sample receipt is several working days including chamber stabilization, weighings, and reporting. Hot plate and manikin testing may require additional scheduling for instrument availability.

Conclusion

Determination of water vapor transmission is the decisive measurement separating a genuinely breathable waterproof hardshell from a simple rain barrier. Reliable results depend on disciplined sampling, strict control of temperature, humidity, and air movement, correct specimen sealing and orientation, and — above all — transparent reporting of the method used, because WVTR values from different standards are not interchangeable. By pairing gravimetric dish or hot plate data with complementary waterproofness testing and durability evaluation, manufacturers and buyers can substantiate performance claims, verify compliance with GB/T 32614, EN 343, and related frameworks, and ultimately deliver outdoor garments that stay dry both from the outside and from within.