MVTR vs RET: Two Ways to Rate Waterproof Breathable Fabrics

The Outdoor Jacket Buyer Who Asked Why His Spec Sheet Had Two Different Numbers

Last autumn, a sourcing manager at a European outdoor apparel brand contacted us with a question that comes up more often than it should. He had received two product data sheets from two different membrane suppliers. The first sheet rated the membrane at MVTR 15,000 g/m²/24h. The second sheet rated its membrane at RET 4 Pa·m²/W. Both sheets claimed “high-performance waterproof breathable.” The sourcing manager wanted to know which membrane was actually more breathable.

When we walked through the two test methods with him, the answer became clear. The two membranes were both high-performance — they were simply rated by two different conventions. The first used the standard MVTR measurement (mass of water vapor through fabric per unit time). The second used the RET measurement (resistance to evaporative heat transfer). The two metrics describe the same physical phenomenon — moisture vapor moving through a fabric — but with opposite numerical conventions. Higher MVTR is better. Lower RET is better.

The confusion was not in the technical data but in the comparison. The sourcing manager had been reading the two numbers side by side and assuming the higher absolute value was the better membrane. Once he understood that the two metrics correlated inversely, the choice became clear: compare each membrane against its own scale, and ask both suppliers to provide the data on the same scale if a head-to-head comparison is required.

Chaoyue New Material has been producing ePTFE micro-porous membranes for textile applications for years. The MVTR vs RET question is one of the most common inquiries we receive from apparel and footwear brands, and the resolution is the same for every buyer: understand what each metric measures, use the right metric for the right application, and compare products on the same scale. This article is the engineering framework behind the two metrics, and it is intended as reference material for outdoor apparel, footwear, and protective equipment buyers who are specifying waterproof breathable membranes for their product lines.

MVTR: The Mass-Based Breathability Metric

MVTR stands for Moisture Vapor Transmission Rate. It is the most widely used metric for measuring the breathability of waterproof breathable fabrics, and the test methods are well-established across the global textile industry. The principle is straightforward: the fabric sample is mounted in a test cup, a controlled humidity is established on one side of the fabric, and the water vapor that passes through the fabric is measured as a mass over a defined time.

The standard test methods for MVRT include the upright cup method (used by ASTM E96 in the US and JIS L1099 A1 in Japan) and the inverted cup method (used for measuring water resistance rather than just moisture vapor transmission). For waterproof breathable membranes in outdoor apparel, the JIS L1099 A1 method is the most commonly cited, because it provides consistent results across a wide range of membrane constructions and is widely accepted by Asian, European, and North American apparel brands.

The result is reported in grams per square meter per 24 hours. A higher number means more moisture vapor passes through the fabric in the same time, which corresponds to better wearer comfort during physical activity. For high-performance waterproof breathable membranes, MVTR values are typically above 10,000 g/m²/24h. For entry-level waterproof breathable fabrics, the MVTR may be between 5,000 and 10,000 g/m²/24h. For non-breathable waterproof fabrics, the MVTR is below 1,000 g/m²/24h.

The ePTFE micro-porous membrane in the Chaoyue catalog is rated at MVTR ≥ 10,000 g/m²/24h per JIS L1099 A1, with the standard product line meeting the high-performance benchmark for outdoor apparel applications. The bi-component variant extends the rating to MVTR ≥ 8,000 g/m²/24h, which is the typical benchmark for protective apparel where durability and tear strength are prioritized over maximum breathability.

RET: The Resistance-Based Breathability Metric

RET stands for Resistance to Evaporative Heat Transfer. It is the metric preferred by the Hohenstein Institute in Germany and is the test standard for European outdoor apparel specifications. The principle is different from MVTR: the fabric sample is mounted on a heated plate that simulates skin temperature, and the energy required to maintain the plate temperature as moisture evaporates through the fabric is measured.

The standard test method is ISO 11092, which is the international standard for measuring thermal and evaporative resistance of clothing. The result is reported in units of Pa·m²/W (Pascal-square meter per Watt). A lower RET value means the fabric presents less resistance to evaporative heat transfer — the moisture vapor passes through more easily, and the wearer feels cooler and drier.

The RET scale is interpreted using comfort classification thresholds. RET values below about 6 Pa·m²/W are considered comfortable for sustained physical activity. RET values between 6 and 13 Pa·m²/W are considered comfortable for moderate activity. RET values between 13 and 20 Pa·m²/W are considered uncomfortable for most wearers. RET values above 20 Pa·m²/W are considered unsatisfactory for breathability applications.

The ePTFE micro-porous membrane is rated at RET values consistent with the high-performance comfort category, corresponding to the MVTR ≥ 10,000 g/m²/24h rating per the relationship between the two metrics. The exact RET value depends on the specific membrane thickness and formulation, and the product data sheet should be referenced for the specific RET value per product code.

The Physics: Why The Two Metrics Are Correlated But Not Directly Convertible

MVTR and RET describe the same physical phenomenon — moisture vapor moving through a fabric — but with different measurement conventions. MVTR measures the mass of moisture vapor per unit time per unit area. RET measures the resistance to heat transfer during evaporation of moisture vapor. The two metrics are correlated because higher moisture vapor permeability corresponds to lower evaporative resistance.

However, the conversion is not direct because the two test methods use different physical setups. MVTR uses a temperature-controlled environment with a humidity gradient across the fabric. RET uses a heated plate at skin temperature with a controlled humidity gradient. The driving forces for moisture vapor transport are different, and the resulting measurements are not linearly scalable.

For accurate comparison between two membranes, the test data should be referenced on the same scale. If the buyer wants to use MVTR as the reference, both membranes should be tested per JIS L1099 A1 or ASTM E96. If the buyer wants to use RET, both membranes should be tested per ISO 11092. Cross-scale conversion introduces error and is not recommended for technical specifications.

The correlation between the two metrics is approximately that a fabric with MVTR ≥ 10,000 g/m²/24h typically has RET ≤ 6 Pa·m²/W, and a fabric with MVTR ≥ 15,000 g/m²/24h typically has RET ≤ 4 Pa·m²/W. These are general trends, not precise conversion factors, and the actual relationship depends on the specific fabric construction.

The Application Mapping: Which Metric To Use For Which End-Use

Different end-use applications favor different test metrics, and the choice of metric affects the supplier data sheet and the buyer specification. For outdoor apparel brands selling primarily in European markets, RET is the more familiar metric because the European outdoor industry has historically referenced the Hohenstein Institute’s comfort classification. For outdoor apparel brands selling primarily in North American or Asian markets, MVTR is the more familiar metric because the test methods are well-established in those markets.

For footwear applications, the MVTR is typically the more cited metric because the JIS L1099 A1 method is widely used in footwear testing. The ePTFE membrane for outdoor textiles in the Chaoyue catalog is rated at MVTR ≥ 10,000 g/m²/24h, which is the typical benchmark for waterproof breathable footwear linings.

For protective apparel applications — firefighting gear, chemical protection suits, military uniforms — the RET metric is often more relevant because the European protective apparel standards reference ISO 11092. The bi-component ePTFE membrane in the Chaoyue catalog is rated at MVTR ≥ 8,000 g/m²/24h, which corresponds to the RET range appropriate for protective apparel. The choice of mono-component vs bi-component membrane is determined by the durability requirements of the application, with bi-component offering higher tear strength but slightly lower MVTR.

For a global product launch that spans European, North American, and Asian markets, the recommendation is to specify both MVTR and RET in the product data sheet, and to verify both values with the test reports from the membrane supplier. The dual specification allows the brand to reference the metric that is most familiar to each regional market.

The Test Equipment And Lab Standards: Which Labs To Use

For commercial product data sheets, the test report should come from a recognized third-party testing laboratory rather than from the membrane supplier’s in-house testing. The recognized third-party laboratories for waterproof breathable fabric testing include SGS, Intertek, Bureau Veritas, and TÜV. The Hohenstein Institute in Germany is the reference laboratory for RET testing specifically.

For OEM buyers specifying waterproof breathable membranes, the test report should be referenced to one of these third-party laboratories, with the test method clearly identified (JIS L1099 A1, ISO 11092, ASTM E96, or equivalent). The test report should include the test conditions (temperature, humidity, duration) and the sample preparation method (number of washes, conditioning time) because these factors affect the measured value.

The Hohenstein Institute in Germany is the historical reference for RET testing and has published the comfort classification scale that is widely used in European outdoor apparel. The Hohenstein label is often cited on European outdoor apparel hangtags, indicating that the garment has been tested per the Hohenstein methodology. SGS and Intertek are the most widely used commercial test labs for general waterproof breathable fabric testing, with global coverage and standardized test protocols.

The Wash Durability Question: How MVTR And RET Change Over Service Life

One of the most overlooked aspects of MVTR and RET ratings is that the values quoted on the product data sheet are typically the initial values — before the fabric has been washed, worn, or exposed to environmental stress. The wash durability of the waterproof breathable coating or membrane determines whether the breathability is maintained over the service life of the garment.

For ePTFE micro-porous membranes, the structure is mechanically stable — the pore network does not collapse under wash cycles or compression. The wash durability is more affected by the surface treatment (DWR — durable water repellent finish) and the laminate bond between the membrane and the face fabric. The Chaoyue bi-component membrane is engineered to maintain its waterproof rating above 10,000 mm hydrostatic head after 5 wash cycles, and the MVTR is maintained within a defined range through the same wash cycle count.

For OEM buyers specifying waterproof breathable membranes, the request should include the after-wash performance values, not just the initial values. A membrane that loses 50% of its MVTR after 20 wash cycles is not equivalent to a membrane that loses 10% over the same cycle count, even if the initial values are identical. The wash durability is what distinguishes a premium-grade membrane from a mid-grade membrane.

The wash durability data is typically generated per the same test methods as the initial values (JIS L1099 A1 for MVTR, ISO 811 for water resistance, ISO 11092 for RET). The membrane supplier should be able to provide the wash durability data per the same test methods as the initial values, with the number of wash cycles clearly documented.

The ePTFE Membrane Specification: What Chaoyue’s Data Sheet Tells You

For OEM buyers specifying the Chaoyue ePTFE micro-porous membrane for textile applications, the standard product data sheet includes the MVTR rating per JIS L1099 A1, the water resistance rating per ISO 811, the water resistance after 5 wash cycles per ISO 811, the membrane thickness, and the weight per unit area. The standard line (RG212, RG213, RG214) provides MVTR ≥ 10,000 g/m²/24h across the thickness range, while the bi-component line (RG222, RG223, RG224) provides MVTR ≥ 8,000 g/m²/24h with higher durability.

The data sheet does not currently include the RET value per ISO 11092, because the European market reference is less common in the current customer base. For buyers who specifically need the RET value, the Chaoyue engineering team can provide the measurement on a sample basis, with the test performed at the Hohenstein Institute or at a third-party test lab with ISO 11092 capability.

For buyers specifying the membrane for protective apparel applications, the key specification values are the water resistance rating (≥ 10,000 mm hydrostatic head for the standard line, ≥ 15,000 mm for the higher-rated product codes) and the durability after wash cycles. The MVTR is typically above 8,000 g/m²/24h for protective apparel applications, which corresponds to the comfort category for moderate to high physical activity.

The Common Specification Mistakes Buyers Make

Across the OEM projects we have supplied, the same specification mistakes show up repeatedly. These are the predictable consequences of common procurement shortcuts, and they are worth flagging because they are entirely preventable.

Specifying MVTR without identifying the test method. The MVTR value alone is not informative unless the test method is identified. MVTR = 10,000 g/m²/24h per JIS L1099 A1 is not the same as MVTR = 10,000 g/m²/24h per ASTM E96, because the test conditions differ. The fix is to always specify both the MVTR value and the test method in the product specification.

Comparing RET values from one supplier to MVTR values from another. The two metrics use different conventions and cannot be directly compared. The fix is to ask both suppliers to provide the data on the same metric, or to compare each metric against its own published comfort classification scale.

Ignoring the wash durability in the specification. The initial and after-wash performance values can differ significantly. The fix is to specify both the initial and after-wash values, with the number of wash cycles clearly documented.

Selecting the membrane based on maximum MVTR alone. A higher MVTR can come at the cost of lower water resistance, lower durability, or higher cost. The fix is to specify all three parameters (MVTR, water resistance, durability) and select the membrane that delivers the best balance for the specific application.

The Standard Bodies And Regulatory Framework

The waterproof breathable fabric industry operates under a combination of voluntary standards and regulatory requirements. The key standards bodies are the JIS (Japanese Industrial Standards) for the JIS L1099 A1 test method, the ISO (International Organization for Standardization) for the ISO 11092 RET test method and the ISO 811 water resistance test method, and the AATCC (American Association of Textile Chemists and Colorists) for the AATCC 127 water resistance test method commonly used in North American apparel specifications.

The AATCC publishes the test methods that are widely cited in North American outdoor apparel specifications. The AATCC 127 water resistance test method is the reference for waterproof claims on North American outdoor apparel, and the AATCC 35 rain test is the reference for rain resistance in light to moderate conditions.

The TAPPI (Technical Association of the Pulp and Paper Industry) publishes the T 530 test method for water vapor transmission rate through paper and paperboard, which is occasionally referenced for film-based waterproof breathable materials. The BSI Group (British Standards Institution) provides the EN 14384 and related European standards for protective clothing for firefighters, which include membrane performance requirements.

Closing Recommendation: Use Both Metrics, On The Same Membrane

For OEM buyers specifying waterproof breathable ePTFE membranes for outdoor apparel, footwear, and protective equipment, the recommendation is to request both MVTR and RET values from the membrane supplier, on the same membrane sample, with the test methods and the test lab clearly identified. The buyer can then reference the metric that is most familiar to the regional market during the product launch, while having both values available for technical comparison and regulatory compliance.

Chaoyue provides the MVTR rating per JIS L1099 A1 as the standard specification across the ePTFE membrane product line, with the option to provide the RET value per ISO 11092 on request for European market references. The wash durability data is available per the standard test cycle count, and the third-party test lab reference is provided with each shipment.

For buyers who want to verify the MVTR and RET values for a specific membrane sample, the Chaoyue engineering team is available for technical consultation. Request the test data with the specific test method, the specific test lab, and the specific membrane sample referenced. The standard response time is within 24 hours, with sample testing and engineering documentation available within the typical OEM procurement timeline.

About the Author: The Chaoyue New Material Technical Team specializes in ePTFE micro-porous membrane engineering for waterproof breathable textile applications, including sportswear, cold weather clothing, outdoor gear, rainwear, specialized protective garments, military and medical uniforms, footwear, and camping equipment. The team’s writing is grounded in production-floor experience and direct technical support for OEM customers across global apparel, footwear, and protective equipment markets.