A single ski jacket carries 20,150 mm on its spec sheet. Tested under another standard, the same jacket carries 23,000 mm. Same garment, same fabric, two true answers. The difference is the standard each was measured under — GB/T 4744-2013 in one case, JIS L 1092:2009 in the other. There is no conversion table between them.
That is what makes ski jacket specs hard to read. You have compared two hangtags assuming like for like. Usually they were not comparable at all.
This piece covers how the numbers are produced and how far to trust them. For the short answer on which rating to buy, see our guide to which jacket construction suits how you ski.
Key takeaways
- A hydrostatic head figure means nothing until the standard behind it is named: one garment returns different results under different standards.
- Breathability runs on two opposing scales — MVTR is higher-is-better, RET is lower-is-better — and neither converts into the other.
- An MVTR number without its method is decoration; one cross-standard test put a single membrane below 1,000 g and above 17,000 g.
- Waterproof fabric is not a waterproof garment. Ask the same five questions of every number.
The Four Numbers on a Label — and the Six That Never Appear
Every claim on a ski garment is shorthand for a lab procedure. Four usually reach the tag:
| Spec | Unit | What the number describes | Printed? |
|---|---|---|---|
| Waterproofness (hydrostatic head) | mm H₂O or kPa | Pressure held back before water broke through at the third point | Almost always |
| Breathability (MVTR) | g/m²·24h | Vapour grams crossing a square metre in 24 hours | Sometimes, rarely with the method |
| Breathability (RET) | m²·Pa/W | How strongly the fabric resists that same vapour flow | Seldom |
| Abrasion resistance | rubs / cycles | Martindale rubs survived before the fabric broke down | Seldom |
And six disclosures decide whether any of them can be compared:
- The full standard number, not just the family name — "GB/T" is a system, "GB/T 4744-2013" is a test.
- Finished garment or flat swatch. Not the same object.
- Before or after laundering. Finishes degrade at different rates.
- Which MVTR method variant. This alone can move a result tenfold.
- Face fabric denier and construction.
- Seam construction beyond the bare word "taped."
Most pages stop at the four. You can compare the full panels across the ski jacket range.
How Ski Jacket Waterproof Ratings Are Actually Measured
The hydrostatic head test — and what a 20K rating really means
A 20K rating means a fabric sample held back a 20-metre column of water before water forced through at three separate points in a hydrostatic head test. That is roughly 196 kPa, or 28 psi. Higher resists more pressure — but only against a number from the same standard.
A fabric disc, usually 100 cm², is clamped over a water chamber. Pressure rises at a controlled rate until three leaks appear on the far side — droplets that never grow do not count. Several specimens get averaged.
That unit also answers to the name Schmerber — one Schmerber being one millimetre of water column. ISO 811, the common reference, raises pressure at 10 ± 0.5 cm or 60 ± 3 cm per minute against water at 20 ± 2 °C or 27 ± 2 °C, across at least five specimens. Warmer water returns lower readings, and different rates need not agree. GB/T 4744-2013 reports kPa with cmH₂O; AATCC 127 differs in the details.
Why no conversion table exists between them
The Daybreak and Rime shells in our line publish two figures: 20,150 mm under GB/T 4744-2013 and 23,000 mm under JIS L 1092:2009. Neither is inflated — same fabric under two rulebooks, with different specimen handling and no agreed arithmetic between them. An awkward number with a standard attached beats a clean round one every time.
Elena learned this in a Chamonix shop one December: one tag read 20,150 mm with the standard beside it, another a confident 20,000 mm with no method anywhere. She bought the second — better fit — but stopped trusting round numbers.
Elena and Jonas are composites, not individual customers.
The standards, side by side
Every hydrostatic head test asks how much water pressure a fabric holds back. That is where waterproof standards part company: each sets its own units, specimen handling and stopping point. Numbers do not travel between them:
| Standard | Issued by | What it tests | Result |
|---|---|---|---|
| JIS L 1092:2009 | JISC | Water resistance: Method A reads column height, Method B a gauge | mm H₂O (A) or kPa (B); spray grades 1–5 |
| GB/T 4744-2013 | SAC, China | Hydrostatic pressure, third seepage point | kPa with cmH₂O |
| ISO 811 | ISO (TC 38); EN ISO 811 in Europe | Resistance to water penetration, 100 cm² specimen | cmH₂O or Pa |
| AATCC 127 | AATCC | Hydrostatic pressure; larger specimens, three minimum | cmH₂O |
| EN 343:2019 | CEN | Rain protection, material and seams, pre-treated for classes 2–4 | Class X (penetration), Y (RET), R optional |
EN 343 differs from the rest: classes instead of a pressure figure, seams as well as fabric, retesting after pre-treatment. A garment claim, not a fabric claim.
What each rating survives
What waterproof rating you need depends less on the forecast than on the pressure your body puts on the fabric — straps, a wet lift seat, a knee in the snow. Find your load and read across:
| Rating | Pressure | What it copes with | Typical pressure source |
|---|---|---|---|
| 5,000 mm | ~49 kPa | Dry snow, short showers | No sustained load |
| 10,000 mm | ~98 kPa | Prolonged snowfall | A pack strap over one shoulder |
| 15,000 mm | ~147 kPa | Wet snow and wind | A knee or forearm in wet snow |
| 20,000 mm | ~196 kPa (28 psi) | Wet snow all day | Body weight on a wet lift seat |
| 30,000 mm+ | ~294 kPa | Loaded, repeated contact | Hip belt plus sitting, all day |
Rain on a sleeve applies almost no pressure; a pack strap applies more, kneeling in wet snow more again. The higher tiers exist for pressure. Which waterproof rating to choose for how you ski is a separate question.
Breathability: MVTR, RET, and Why the Unit Decides the Answer
MVTR counts how many grams of water vapour cross a square metre of fabric in 24 hours, so higher is better. RET measures how strongly the fabric resists that same vapour escaping, in m²·Pa/W, so lower is better. Two scales, one property, opposite directions — and neither converts into the other.
Confuse them and you will read the best hardshell on the page as the worst one.
What MVTR means, and why it is not one test
MVTR counts vapour grams crossing a square metre in 24 hours, and it is measured by a family of cup methods. The members disagree violently. Fabric is stretched over a cup holding water or a drying agent, upright in some versions, inverted in others so liquid sits against it. Each runs in a different climate, from ASTM E96 variants at 23 °C and 50 % RH to JIS L 1099 A-1 at 40 °C and 90 % RH.
In April 2025, membrane developer dimpora ran one membrane through six standards. It returned 10,200 g/m²·24h under JIS L 1099 A-1 and 900 g/m²/24h under ASTM E96 B — a spread from below 1,000 g to above 17,000 g. Across 154 measurements repeatability held at 7 %: what broke was the comparison.
An MVTR figure with no method tells you nothing — and since JIS-derived methods return far higher figures than ASTM ones for identical material, a brand quoting JIS is not necessarily selling a more breathable shell, only a more generous test.
MVTR bands track effort rather than conditions — how hard you are working decides where you land. Read down until you reach your usual day on the hill:
| MVTR band | What it copes with |
|---|---|
| Below 10,000 g/m²·24h | Cruising pisted runs, standing around |
| 10,000–20,000 g/m²·24h | Continuous piste skiing, moderate touring climbs |
| Above 20,000 g/m²·24h | Skinning uphill, bootpacks, sustained output |
RET: the scale that runs backwards
RET comes from ISO 11092, the sweating guarded-hotplate test: a porous plate held at skin temperature is fed water so it sweats, the fabric lies across it, and the instrument records the power needed to hold that temperature as vapour escapes. Results arrive in m²·Pa/W.
Because it models wearing the fabric rather than sealing it over a cup, RET figures from different labs are broadly comparable — which is why EN 343 grades breathability in RET.
| RET value | Industry reading |
|---|---|
| Below 6 | Extremely breathable |
| 6–13 | Very breathable |
| 13–20 | Breathable |
| 20–30 | Unsatisfactory for active use |
| Above 30 | Effectively not breathable |
Those bands are an industry convention traceable to the Hohenstein Institute, not part of the ISO text, so treat a value near a boundary as exactly that.
Why warmth and breathability pull apart
The barrier that stops liquid water under pressure also resists vapour leaving. Published figures make it concrete: an insulated shell in our line returns 7,430 g/m²·24h, while the Dermizax 3L Pro, tested to JIS L 1099:2021, returns 21,372 g/m²·24h. And the warmest garment we publish, rated −35 °C, is also the least waterproof once washed, down 16.1 %.
The way out is moving insulation into its own layer, which is why how to layer for skiing matters more than any number here.
Seams, Zips and the Leaks That Never Show Up in the Fabric Number
Waterproof fabric is not a waterproof garment, and the gap between the two is mostly stitching.
Fully taped vs critically taped seams: what actually changes
Fully taped means every sewn seam is covered with heat-bonded tape pressed over the needle holes. Critically taped means only the most exposed seams — hood, shoulders, neck, armholes — are covered. Elsewhere the fabric alone does the work.
Every stitch punches a hole. A 30,000 mm membrane achieves nothing if water can walk through three hundred of them.
| Factor | Fully taped | Critically taped |
|---|---|---|
| Coverage | Every seam | Exposed seams only |
| Weight and cost | Heavier, pricier | Lighter, cheaper |
| Fails first at | Face fabric or closures | Untaped seams under contact |
| Suits | Wet snow, all-day resort use | Dry climates, weight-focused touring |
Try this in a shop: sit down. A rider on a soaked chairlift holds body weight on one seam line for minutes at a time, perhaps ten times a day. That is what separates the two constructions. Not rainfall.
Zips deserve the same suspicion. The water-repellent zips on our own 3L shell, YKK AquaGuard® among them, are not watertight alone; the storm flap behind them does the real work. The best breathability control is no membrane: an open pit zip dumps more vapour in a minute than a top-tier fabric moves in an hour.
Construction is also why ski pants fail differently from jackets: different pressure points, different failure order.
Abrasion, Denier and Fabric Construction: What Decides Year Three
Denier measures the mass of one filament in grams per 9,000 metres of yarn, so higher means thicker and heavier. And 2L, 2.5L or 3L describes how many layers are bonded into the shell panel — not how warm the garment is.
The Martindale test — what a cycle actually is
GB/T 21196.2-2007 rubs a circular specimen against standard wool abradant in a Lissajous figure — a figure-eight imitating multi-directional wear. Load is set by category: 12 kPa for workwear, 9 kPa for clothing textiles, 3 kPa for coated fabrics. Specimens are conditioned at 20 ± 2 °C and 65 ± 4 % RH, and the test stops when threads break.
Read that carefully: it records when the fabric broke, not when the membrane stopped working — a laminate can look untouched while delaminating underneath. Multiples need care too. One shell we publish reports abrasion as roughly 15 times the national standard requirement. Honest, still not comparable, because "the requirement" depends on the category it is benchmarked against.
Denier, in plain numbers
20D is fine and light, 40D the workhorse of ski shells, 70D and above is reinforcement territory: shoulders, cuffs, seat panels. Denier describes the yarn, not the fabric: weave density and finishing matter too, which is why brands skip it. Unprinted, you cannot judge whether a shell survives three seasons.
2L vs 3L ski jacket: what the layers actually change
Before choosing between them: the labels 2L, 2.5L and 3L describe how the membrane is backed, not how warm the garment is. That choice shows up mostly in weight and wear. Compare the three:
| Layer | 2L | 2.5L | 3L |
|---|---|---|---|
| Structure | Face + membrane with a separate hanging liner | Face + membrane + thin sprayed backer | Face + membrane + bonded tricot backer |
| Feel | Softest, needs a liner | Lightest, faintly papery | Stiffest, most substantial |
| Wear | Liner absorbs the rubbing | Backer can wear through first | Backer protects the membrane best |
| Typical use | Insulated, lifestyle-leaning jackets | Packable shells | Resort and backcountry hardshells |
Warmth is a separate question — an insulated 2L can be warmer than an unlined 3L — and it is answered elsewhere. What the layer count changes here is what happens at the test endpoint. The fabric-side story is in how the shell fabric itself is built.
DWR: The Spec That Fails First
DWR is the finish you will notice failing before anything else, and almost no one prints a grade for it.
What does DWR stand for, and what does it actually do?
DWR stands for Durable Water Repellent — a finish applied to the face fabric that lowers surface tension so water beads and rolls away instead of soaking in. It barely affects the hydrostatic head number, and it is the first thing to go.
Jonas had three seasons out of his shell, then washed it in whatever was under the sink, tumbled it warm and flew to Niseko. By the second lift of day one, in moderate wet snow, the shoulders had gone the grey of a wet paper towel. He spent the trip convinced the membrane had failed.
Nothing had leaked. The face fabric had wet out, and saturated face fabric is a wall — vapour had nowhere to go, so sweat sat against his base layer and read as dampness. A bottle of technical wash later, it beaded again.
Remember the mechanism: when the face fabric saturates, breathability stops working. A ventilation failure and a waterproofing failure feel identical from the inside.
GB/T 4745-2012 measures this with a spray test, grading how much the surface wets — Grade 5 at the top meaning no wetting and no droplets adhering. The Dermizax 3L Pro publishes Grade 5 initial. Note the word initial. Most current finishes are C0, fluorine-free — right environmentally, generally shorter-lived than the old chemistry, and the first thing you should be maintaining.
How to Re-Waterproof a Ski Jacket
Most "dead" jackets recover in an afternoon. The sequence matters more than the product.
- Wash it properly. A technical cleaner for waterproof fabrics, not household detergent — soap residues attract water.
- Rinse twice. Trapped residue is the single most common cause of a failed reproof. A second rinse costs two minutes and decides whether the finish can bond at all.
- Apply while damp. Wash-in covers everything, including inside seams; spray-on targets panels. Respect the label's dwell time.
- Heat-activate. Twenty minutes low tumble, or a cool iron with a cloth between iron and fabric. Heat realigns the finish.
- Test it. Run water on the shoulder. Beading means done; a dark flat patch means repeat once.
Why step four gets skipped. Most people treat reproofing as the last stage of washing, so the jacket goes from the machine straight to the drying rack. Heat is a separate operation with its own job, and it is the one that decides whether the finish works at all.
When reproofing is not the answer. If the shoulders still darken after two full cycles, the finish is not the problem. A laminate can delaminate while the face fabric still looks new, and nothing you wash on will reach the membrane.
Wash-in or spray-on
Wash-in is the better first move when the whole outer has stopped beading, reaching seam tape edges a spray misses. Spray-on earns its place when protecting loft underneath, or when only high-wear zones have given up — pack-strap shoulders, hood crown, cuff edges. Both need heat; skipping step four is why most home reproofs disappoint.
What not to do
Never use ordinary detergent or fabric softener, which coats fibres in a water-loving film. Never reproof a dirty jacket — you seal the dirt in. Never iron without a cloth. Never spot-treat one shoulder and stop; uneven surface tension makes the rest wet out faster. Read the care label first.
How to Compare Ski Jacket Specs: Five Questions Before You Trust a Number
The five questions to ask of any spec sheet, ours included:
- Tested on the finished garment, or on a fabric swatch?
- Measured before laundering, or after?
- Which standard number, with its year?
- Breathability published, and with which method?
- A readable report, or just a marketing number?
1. Finished garment, or fabric swatch? A flat swatch has no seams, no curves, no under-arm gusset, no zip behind a flap. Our listing for the Dermizax 3L Pro states its figures were measured on the finished garment — the rare choice worth asking for.
2. Fresh, or after laundering? Across our own published range — measured on the same rig, before and after laundering — the spread runs like this: Skyline CORE loses 1.1 %, Black Knight 9.6 %, 3L Thick with RECCO 11.6 %, 3L Fully Padded 16.1 %. Those figures do not specify wash cycles, so treat them as directional — and mind the counter-example, where 3L Color Hardshell's MVTR rose after washing, from 11,200 to 13,800. A range that wide on one brand's own line is why the after-laundering figure belongs on every spec sheet, ours included.
3. Which standard number, exactly? "GB/T" is a family name, not a method. GB/T 4744 measures hydrostatic head; GB/T 4745 measures surface repellency — one acronym, two unrelated properties.
4. Is breathability published, and with its method? A shell printing 34,570 mm with nothing about vapour movement has given you half a picture. The Dermizax 3L Pro pairs it with 21,372 g to JIS L 1099:2021; the method name is what makes a number usable.
5. Can you actually read a report? A figure inside a marketing graphic is not a report. Look for the standard number, whether the sample was garment or fabric, conditioning, and a date. Very few brands publish a scan — we do not either. The minimum bar is the standard's name: without it there is nothing to check the number against.
Some numbers resist comparison entirely. Comfort temperature is one: the Dermizax 3L Pro carries −15 °C, but no universal method sits behind such ratings, so treat them as an internal estimate rather than a measurement.
Take the five questions to the ski jackets we publish full panels for, then to any other spec sheet you find.
Quick Reference: How to Read a Ski Jacket Spec Sheet in 60 Seconds
A round number here, a missing method there — the patterns repeat. Learn what each signals and reading a ski jacket spec sheet takes under a minute — otherwise it is guesswork. Five to look for:
| What you see | What it tells you | Ask next |
|---|---|---|
| Round number, e.g. "20,000 mm" | A rounded claim, not necessarily a measured result | Which standard produced it? |
| Precise number, e.g. "20,150 mm" | Someone ran a test and reported it honestly | Which year's standard, on garment or fabric? |
| "GB/T tested" with no suffix | Almost nothing — GB/T is a family of dozens of methods | 4744 or 4745? Full number, please |
| High MVTR, no method | Nothing comparable | JIS L 1099 A-1, B-1, or ASTM E96? |
| No after-wash figure anywhere | It is a first-day number | What is it after ten washes? |
FAQ
What does 20K/20K mean on a ski jacket? It claims the fabric resists a 20-metre water column and transmits 20,000 g/m²·24h of vapour. Both are usually rounded, and both become comparable only once the standard and MVTR method are named.
Can I convert MVTR into RET? No. The scales come from different apparatus under different vapour pressure gradients — MVTR counts throughput, RET measures resistance — and no conversion factor exists.
Why do two brands publish different numbers for what looks like the same fabric? Four usual causes: different standards, different method variants, a fabric swatch instead of a garment, or a figure taken before rather than after laundering.
Does a higher hydrostatic head always mean better protection? No. Past roughly 20,000 mm you are buying resistance to pressure rather than weather, and every step up costs breathability, weight or suppleness.
Do I need fully taped seams? Yes if your skiing includes wet lift seats, kneeling or a loaded pack. If you ski dry snow and count grams, critically taped will do and costs less.
How do I know my DWR has failed? Run water on the shoulder. Beading means it works; fabric that darkens and absorbs has lost its finish — long before anything leaks through. Reproof at that point.
Numbers Are the Result. Method Is the Fact.
Everything above reduces to one habit: never accept a performance number without its provenance. Ask for the standard in a shop and you will usually get a shrug, which is itself an answer. On a product page it is one line of text — the cheapest thing a brand can print, and the one most of them leave out.
Learn those five questions and you will read a spec sheet faster than the salesperson beside you. Numbers you cannot date, place under a standard or trace to a method belong with round numbers — fine to admire, useless to compare.
