Waterproof and Breathability Ratings Explained
A 20,000 mm waterproof rating means the fabric held back a 20 metre column of water in a lab; a 20,000 g/m²/24h breathability rating means vapour passed through a square metre in a day. Both are useless without the test method attached.
Here is the short version. Waterproofing is measured as hydrostatic head in millimetres, usually to ISO 811, and roughly 10,000 mm handles sustained rain. Breathability is measured as moisture vapour transmission in g/m²/24h, or as RET resistance, and there are at least five common methods that produce wildly different numbers from the same piece of fabric. Two jackets quoting different methods cannot be compared, and most brands do not tell you which one they used.
What the waterproof number actually measures
Hydrostatic head is a simple, physical test. You clamp a piece of fabric, push water against one side at a controlled rate, and record the pressure at which water forces its way through. The result is expressed as the height of a water column the fabric resisted. A 20,000 mm rating means it held back the equivalent of twenty metres of water stacked above it.
The dominant standard is ISO 811, which specifies the rate of pressure increase and the water temperature. The American equivalent, AATCC 127, uses a different rate. Faster pressure ramps give higher numbers, so an ISO 811 result and an AATCC 127 result on the same fabric will not match.
For rough calibration, and these bands are conventions rather than standards:
| Hydrostatic head | What it copes with |
|---|---|
| Under 5,000 mm | Light showers. Water-resistant rather than waterproof |
| 5,000 to 10,000 mm | Moderate rain, short exposure, low activity |
| 10,000 to 20,000 mm | Sustained rain, wind-driven rain, pressure from pack straps and sitting |
| Above 20,000 mm | Prolonged heavy rain, kneeling, sitting on wet ground, heavy loads |
Pressure matters more than most people expect. Rain alone does not push very hard, but a rucksack strap over a wet shoulder, a knee on wet ground, or simply sitting on a damp bench concentrates force on a small area. That is why the difference between 5,000 mm and 20,000 mm shows up in real use even though rain never approaches either figure by itself.
There is also a category of result that looks like a number but is not one. When a test is run to a fixed threshold and the sample passes it, the report says "exceeds 20,000 mm". That is a floor. The true value could be 20,100 or 45,000, and the report does not know. Our own shell falls into this category, and we say so on our lab tests page rather than inventing a headline figure.
The breathability problem: five methods, one unit
Breathability is where the industry quietly falls apart. The unit g/m²/24h looks standard. The methods behind it are not.
| Method | How it works | Effect on the number |
|---|---|---|
| JIS L 1099 A-1 | Upright cup, calcium chloride desiccant, dry conditions | Conservative. Lowest of the g/m²/24h family |
| JIS L 1099 B-1 | Inverted cup, potassium acetate, fabric in contact with liquid | Aggressive. Commonly several times an A-1 result on the same fabric |
| ASTM E96 procedure B | Inverted cup, water | Mid range, not interchangeable with JIS |
| ASTM E96 procedure BW | Inverted, fabric in contact with water | Higher than procedure B |
| ISO 11092 (RET) | Sweating hot plate. Measures resistance, so lower is better | A different unit entirely. Cannot be converted to g/m²/24h |
Two consequences follow, and they are the whole reason this article exists.
First, a brand can move its breathability number substantially without changing the fabric at all, simply by testing to a more generous method. Nothing about that is fraudulent. It is just a choice, and one that is rarely disclosed.
Second, RET and MVTR are not two ways of saying the same thing. RET measures evaporative resistance on a heated plate that simulates sweating skin. A lower RET is better. Below about 6 is generally treated as very breathable, and under 13 as reasonably breathable. There is no conversion factor between RET and g/m²/24h that survives contact with real fabrics, and any chart offering one is making it up.
What three brands actually publish
We checked what the manufacturers themselves say, on their own sites, in August 2026. The pattern is instructive.
| Brand | Waterproofing published | Breathability published |
|---|---|---|
| W. L. Gore (GORE-TEX) | No hydrostatic head figure published. Gore describes a rain tower test to DIN EN ISO 24231 and its own centrifugal and walking-simulator tests | RET, described as resistance to moisture vapour transfer |
| Sympatex | Water column stated as "over 45,000 mm". The standard used is not named on the page | No MVTR or RET figure published on the technical Q&A page |
| VEAR | At least 20,000 mm, ISO 811:2018, censored at the test threshold | 20,881 g/m²/24h, JIS L 1099:2021 method B-1 |
These figures are not comparable with one another. They come from different test methods, and in two cases from tests the brand has not named. Sources checked 19 August 2026.
Look at what that table cannot tell you. You cannot say whose fabric is more waterproof, because Gore does not publish a water column and Sympatex does not say how theirs was measured. You cannot say whose is more breathable, because Gore publishes a resistance value and we publish a transmission value and there is no bridge between them. Every "GORE-TEX vs everything else" comparison table you have ever seen was built by putting incompatible numbers in adjacent columns.
There is a reasonable defence of Gore's position here, incidentally: they argue that a fabric number does not predict whether a finished garment keeps you dry, which is true, and they test complete garments instead. We think that is a fair criticism of the whole numbers game, including our own numbers.
Membrane numbers are not garment numbers
Even a well-labelled fabric figure describes a flat piece of material in a clamp. A jacket is not that. Water gets in through the parts the test never touches.
- Seams. Every stitch is a hole. Unless seams are taped or welded, a 20,000 mm fabric makes a jacket that leaks along its shoulders. Seam taping is the single biggest gap between a fabric spec and a garment's behaviour.
- Zips. A standard zip is not waterproof. Storm flaps, welded zips and internal baffles all address this differently and all add bulk or cost.
- Cuffs, hem and hood. Water runs down and finds openings. This is geometry, not fabric.
- Wet-out. When the outer face fabric saturates, the membrane or coating underneath stops passing vapour outward even though it is still holding liquid water back. The jacket feels like it is leaking. It is not. It has stopped breathing, and you are condensing inside it.
Wet-out is the reason DWR exists. The durable water repellent finish on the face fabric makes water bead and run off so the fabric never saturates. DWR wears off with use and washing, which is why a two-year-old jacket that "stopped being waterproof" has usually just stopped repelling. We cover the fix in how to wash a waterproof jacket.
How to actually use these numbers when buying
Given all of the above, here is what we think the numbers are still good for.
- Use waterproof ratings as a floor, not a ranking. Decide what you need, 10,000 mm for city rain, 20,000 mm if you carry a pack or sit on wet things, then stop comparing above that line. The difference between 20,000 and 28,000 will never be the reason you get wet.
- Only compare breathability within a method. If two brands both publish JIS L 1099 B-1, compare them. If one publishes RET and the other g/m²/24h, you have no comparison and should stop pretending you do.
- Treat an unnamed method as an unknown. A number without a standard is marketing, not data.
- Ask about seams before you ask about fabric. Taped seams change more outcomes than another 5,000 mm of head.
- Weight the ventilation. Pit zips, a two-way front zip and open cuffs move more moisture in real use than any membrane does. Mechanical venting beats material breathability when you are working hard.
| Claim | Value | Standard and method | Source | Checked |
|---|---|---|---|---|
| VEAR shell hydrostatic head | At least 20,000 mmH₂O, censored | ISO 811:2018 | SGS SL92319280247401TX-1 | 21 Jun 2023 |
| VEAR shell vapour transmission | 20,881 g/m²/24h | JIS L 1099:2021 B-1 | SGS SL92319291510201TX | 19 Jun 2023 |
| Gore hydrostatic head | Not published | n/a | goretexprofessional.com quality and testing | 19 Aug 2026 |
| Gore breathability metric | Expressed as RET | RET, ISO 11092 family | goretexprofessional.com quality and testing | 19 Aug 2026 |
| Sympatex water column | Over 45,000 mm | Standard not named on source page | sympatex.com Q&A | 19 Aug 2026 |
A performance number without its test method is not a specification. It is a claim. Ask which standard, which method variant, and whether the figure describes the fabric or the finished garment, and most comparison tables collapse.
Where VEAR sits
Our travel shell is a coated 100% polyester textile, tested by SGS in June 2023. Hydrostatic head came back as "exceeds 20,000 mm" on all five specimens under ISO 811:2018, which means at least 20,000 mm with no measurement above that. Water vapour transmission came back at 20,881 g/m²/24h under JIS L 1099:2021 method B-1, which is the inverted-cup method and therefore a generous one. We publish the method because publishing the number alone would be misleading.
What we do not claim: we have no air permeability test, so we make no laboratory-backed windproofing claim. We have no PFAS testing, so we make no PFAS statement in either direction. And these results cover the VEAR Jacket and VEAR Pants shell only, not the winter products. The full reports, including everything they do not cover, are on the test data behind that figure.
Quick glossary
- Hydrostatic head: the water column height a fabric resists before leaking, in millimetres.
- MVTR: moisture vapour transmission rate, in g/m²/24h. Higher is more breathable, within a single method.
- RET: evaporative resistance from a sweating hot plate test. Lower is more breathable. Not convertible to MVTR.
- DWR: durable water repellent, a surface finish that makes water bead off the face fabric.
- Wet-out: when the face fabric saturates and the jacket stops breathing, which feels like leaking.
- Seam taping: sealing stitch holes with bonded tape, without which fabric ratings do not describe the garment.
Frequently asked questions
Is 10,000 mm waterproof enough for everyday rain?
For walking around a city in rain, yes. 10,000 mm handles sustained rainfall comfortably. You will want more if you carry a loaded rucksack, kneel or sit on wet ground, or spend hours out in wind-driven rain, because those apply localised pressure the rain itself never does. Above roughly 20,000 mm the extra rating stops changing outcomes.
Why do two jackets with the same breathability number feel so different?
Usually because the numbers came from different test methods. JIS L 1099 B-1 returns much higher figures than JIS L 1099 A-1 or ASTM E96 procedure B on identical fabric. Fit, ventilation and how wet the outer face gets also matter more in practice than the fabric figure, since a saturated face fabric stops passing vapour regardless of its rating.
Can you convert RET to g/m²/24h?
No. RET measures resistance on a sweating hot plate under ISO 11092; MVTR measures mass of vapour passing through a cup test. They describe related physics through different apparatus, and no conversion holds across different fabric constructions. Any chart offering an equivalence between the two is approximating something that does not have a stable relationship.
What does "exceeds 20,000 mm" mean on a test report?
It means the test was run up to a 20,000 mm threshold and the sample had not failed when the test stopped. It is a floor, not a measurement. The real figure could be marginally higher or far higher, and the report does not say. Treat it as "at least 20,000 mm" and do not rank it against another brand's precisely measured number.
Does a high waterproof rating mean the jacket will keep me dry?
Not on its own. Fabric ratings describe a flat sample in a clamp. Water enters real garments through untaped seams, standard zips, cuffs and hoods. And when the outer fabric saturates, moisture from your own body condenses inside. Seam construction, ventilation and DWR maintenance affect whether you stay dry at least as much as the headline millimetre figure.
Keep reading
- Softshell vs hardshell for travel: which construction suits which trip.
- Packable vs structured travel jackets: what you give up to make it fold small.
- How to wash a waterproof jacket: restoring DWR before you replace the jacket.
- Cycling to work in the rain: where breathability numbers get tested hardest.
- All comparison and materials guides and the practical travel wardrobe.