Waterproofness & Breathability Ratings - what they mean and how to read them.

You're flipping through waterproof jackets: in a store, on a product page, wherever. Every hangtag has the some numbers: "20,000 / 15,000.." They look authoritative. They supposedly tell you how well the jacket keeps rain out and sweat in check.

The first number is how tall a column of water the fabric holds back before it leaks. The second is usually how many grams of vapor escape through one square meter in 24 hours. But there is a catch.

The First Number: Waterproofness

This one is actually honest.

The test is the hydrostatic head method (ISO 811:2018, with equivalents EN 20811 and JIS L 1092). A fabric sample is clamped flat over a test head, water is applied to the underside and pressure rises at exactly 10 cm H₂O per minute. The test stops the moment three separate drops penetrate the upper surface. The pressure at that point (measured in millimeters of water column) is the rating.

"20,000" means 20,000 mm, about 20 meters of water pressure before failure.

In the real world: standing in the rain puts about 1,000 mm of pressure on your gear. Sitting on a wet seat cranks that to 10,000–13,000 mm. A 20k rating means the fabric keeps water out in any riding condition. Just make sure your seams and zippers are sealed.

The standard is singular and consistent. Numbers from different brands are genuinely comparable. The waterproof number is the time the hangtag tells the full truth.

The Second Number: Breathability

Here the story gets complicated.

The second number represents how easily water vapor (sweat) escapes through the fabric. Depending on the brand, the hangtag might label it:

MVP: Moisture Vapor Permeability
MVTR / WVTR: (Moisture) Water Vapor Transmission Rate
RET: Resistance to Evaporative Transfer

The most common unit is g/m²/24h: how many grams of vapor pass through one square meter in 24 hours. Higher means more breathable.

RET (from ISO 11092) flips the direction: it measures resistance to vapor. Lower RET means more breathable.

The Problem: Dozens of Standards, Zero Consensus

Unlike waterproofness, breathability has no single agreed test. The same fabric, tested under different standards, produces wildly different numbers. Even within one standard, different sub-procedures (different temperatures, humidity levels, cup orientation) are explicitly not expected to match.

Brands pick whichever standard makes their number look best. Most don't state which one they used, or bury it deep in a specsheet.

Standards Reference Table

The table below covers the major standards you will encounter on datasheets and spec sheets.

Standard	Origin	What it reports	How the test works	Typical behavior	Where it's used	Key gotcha
ASTM E96 / E96M (Procedures A, B, BW, C, D, E)	ASTM (USA)	WVTR / permeance (g/m²·24h)	Seal fabric over a cup with water or desiccant; put in controlled air; weigh over time.	Higher temperature and bigger humidity difference usually reads higher. Procedure choice can flip results.	Outdoor apparel, building wraps, general materials	Report the exact procedure + temp + RH or the number is meaningless.
ISO 15496:2018	ISO (international)	Water vapor permeability	"Simple" textile method for factory quality control.	Not designed to compare across brands; only for consistency within one plant.	Textile mills, in-house QC	ISO explicitly states it is not for physiological or PPE classification.
JIS L 1099:2021 (A-1, A-2, B1, B2, etc.)	JIS (Japan)	Water vapor transmission (g/m²·24h)	Multiple cup styles, single/double membrane setups. Built from ISO methods with Japan-specific tweaks.	Method choice matters a lot; hotter/stronger gradients often read much higher than room-temp cup tests.	Outdoor textiles and Asian testing labs	JIS L 1099 is a family of methods. Always state which sub-method (A-1 vs B1, etc.).
BS 7209	BSI (UK)	Water vapor permeability index (%)	Cup test on a moving/rotating setup; result is an index vs a control fabric, not an absolute WVTR.	Relative index simplifies in-lab comparisons but cannot be equated to g/m²·24h figures.	UK/EU apparel testing (historically common)	Reports an index, not a transmission rate.
AATCC TM204	AATCC (USA)	Relative rate of vapor transmission	Textile-focused ranking method for comparing fabrics.	A ranking tool, not an absolute physics number.	Apparel, softgoods, textile labs	Do not mix TM204 results with ASTM E96 numbers; different scale and intent.
GB/T 12704.1	China (GB/T)	Moisture permeability	"Moisture absorption" style method for fabrics.	Settings differ from ASTM/JIS; values do not line up across standards.	China-based sourcing, compliance testing	Often referenced inside China PPE/textile requirements.
GB/T 12704.2 (Method A upright, Method B inverted)	China (GB/T)	Water vapor transmission of fabrics	Water method with upright and inverted cup approaches.	Method B (inverted) is specified for waterproof-breathable laminated materials.	Functional fabrics, coated/laminated textiles	Method B is the one most relevant to membrane-laminate gear.
ISO 11092:2014 (Sweating Guarded Hotplate / "skin model")	ISO	RET (m²·Pa/W) + thermal indices	A heated plate "sweats"; fabric sits on top; the meter reads how hard it is for vapor to escape.	Lower RET = more breathable (opposite direction from WVTR). Great for comfort prediction.	Apparel comfort, PPE evaluation	Not the same unit as WVTR. A "good" RET is below 13; elite membranes are below 6.
ASTM F1868 (Sweating Hot Plate)	ASTM (USA)	Evaporative resistance + thermal resistance	Same "sweating hot plate" concept as ISO 11092, for clothing materials and systems.	Resistance metric; not directly comparable to cup-based WVTR.	Protective clothing, comfort research	Companion to ISO 11092 in protective gear specs.
ISO 12572:2016 (buildings)	ISO	Permeance / permeability (μ, Sd)	Cup tests for building materials under defined conditions.	Strongly dependent on which "cup condition set" is used.	Housewraps, roofing underlayments, vapor control layers	This is the standard behind Sd-value workflows in construction.
EN 1931	CEN/EN (Europe)	Moisture flow rate for waterproofing sheets	European method for roofing/waterproofing membrane sheets.	Built for construction products, not clothing comfort.	Roofing membranes, EU building products	Irrelevant to jacket hangtags but sometimes copied onto datasheet footers.
ISO 2528:2017	ISO	WVTR (sheet materials)	Gravimetric dish/cup for sheet materials.	Not recommended for very low WVTR (high-barrier materials).	Films, membranes as sheet material	Prefer instrumental methods when WVTR is extremely low.
ASTM F1249 (Modulated IR sensor)	ASTM (USA)	WVTR (instrumental)	Two chambers divided by sample; IR sensor detects vapor that passes through.	Better than cup methods for very low WVTR; avoids edge-leak and weighing errors.	Packaging films, barrier laminates, thin membranes	Often uses MOCON-style instruments in labs.
ISO 15106-2:2003 (IR detection, plastics)	ISO	WVTR (instrumental)	Instrumental IR sensor for plastic films and multilayer structures.	Same "good at low WVTR" advantage as ASTM F1249.	Packaging films, polymer membrane layers	Common when the membrane is treated as a plastic film component.
DIN 53122-1	DIN (Germany)	WVTR	Gravimetric cup/dish WVTR, common in EU packaging contexts.	Same limits as other gravimetric methods at very low WVTR.	Films, flexible packaging; sometimes cited for membranes	Often cited as "DIN WVTR" by suppliers.
ASTM E398 (Dynamic RH measurement)	ASTM (USA)	WVTR (dynamic)	Dynamic method measuring vapor transfer through a barrier; result is convertible to standard WVTR units.	Has a practical lower limit affected by seal leakage in instruments.	Barrier films, some membrane testing	Not a cup test; instrument seal quality directly affects accuracy at low WVTR.
ASTM D1653 (Organic coating films)	ASTM (USA)	Water vapor transmission of coating films	Cup-style WVTR for paint, varnish, and lacquer films; free film or on a porous substrate.	Numbers can differ from E96 because the scope and material behavior differ.	Coated fabrics, finishes, coatings R&D	Coating-focused; do not compare directly to E96 results from the same material.

All are legitimate. None of their numbers are directly interchangeable.

The only numbers worth comparing are those measured under the identical standard, sub-procedure, temperature, and relative humidity.

RH (relative humidity) is the percentage of moisture already in the test air versus the maximum it can hold at that temperature. Labs typically run at 50% RH. Push it to 70% and the air is wetter, so less vapor moves through the fabric; WVTR drops, making the same material look less breathable. Same fabric, different RH, different number.

The Diversity Problem

Seventeen standards in the table above, and there are more.

Seems that for some organizations writing a new standard was easier than adopting an existing one. Some exist for good reason: different industries, materials, climates, or test equipment. Others exist only because of inertia or regional politics.

Even if you know the test standard, you can't compare numbers across brands if their methods differ. And a naked number with no test listed? Completely pointless.

The Verdict: Do These Numbers Matter?

Yes, if:

You're checking waterproofness. Hydrostatic head (mm) is actually useful, and it does map to real riding: drizzle vs storm.
You're comparing like-for-like. Same brand, or the same test standard (and ideally the same lab/setup).

No, if:

You're comparing Brand A to Brand B. They may be using different standards, or even the same standard in different ways.
You're looking at breathability numbers without the test details. If the hangtag doesn’t state the standard and conditions (temperature/RH), treat the number as marketing. You can’t compare it across brands, and there’s little enforcement.

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