Breathability is measured two ways: MVTR (moisture vapor transmission rate, in g/m²/24h — higher is better) and RET (resistance to evaporative heat transfer — lower is better). MVTR counts how much water vapor passes through a fabric in a day; RET measures how much the fabric resists letting sweat escape. A jacket can carry one or both numbers, and they don’t convert cleanly because they come from different test methods.
For B2B buyers, breathability is the spec that decides whether a waterproof jacket is comfortable or a sweat-box. As a factory speccing membranes across our shell lines, we see buyers obsess over waterproof ratings and ignore breathability — then field complaints about clammy jackets. Here’s how to read both numbers.
Breathability in One Sentence
MVTR and RET both describe how easily sweat vapor escapes a fabric — MVTR as a throughput (higher = more breathable), RET as a resistance (lower = more breathable).
MVTR (Moisture Vapor Transmission Rate)
MVTR is the most common consumer-facing number, expressed in g/m²/24h — grams of water vapor passing through one square meter of fabric in 24 hours.
| MVTR (g/m²/24h) | Breathability |
|---|---|
| <5,000 | Low — casual rain only |
| 5,000–10,000 | Moderate — light activity |
| 10,000–15,000 | Good — active outdoor |
| 15,000–20,000+ | Excellent — high-output |
The catch: MVTR is measured by several different test methods (upright cup, inverted cup, sweating hotplate) that produce different numbers for the same fabric. Always ask which method a quoted MVTR used before comparing two fabrics.
RET (Resistance to Evaporative Heat Transfer)
RET is the lab-grade standard (ISO 11092, “sweating guarded hotplate”), preferred by technical brands because it’s method-consistent. Lower RET = more breathable.
| RET | Breathability |
|---|---|
| 0–6 | Extremely breathable |
| 6–13 | Very breathable |
| 13–20 | Breathable |
| 20+ | Low breathability |
Because RET is far less method-dependent than MVTR, it’s the more reliable number for comparing membranes apples-to-apples.
The Test Methods Behind the Numbers
- ASTM E96 — common cup-method MVTR (US)
- JIS L1099 — Japanese MVTR methods (A1, B1, etc.) — B1 gives high numbers
- ISO 11092 — RET sweating hotplate (lab standard)
Two fabrics can both claim “20,000 MVTR” while one used JIS L1099 B1 (generous) and the other ASTM E96 (conservative). This is the single biggest source of breathability spec confusion.
Breathability vs Waterproofing — The Trade-Off
Breathability and waterproofing pull against each other: a tighter membrane resists water better but breathes less. The best membranes optimize both, which is why 3-layer laminates with high-end membranes cost more. For a complete picture of how breathability fits other specs, see the hardshell buyer’s guide.
Which Numbers to Spec
| Jacket type | Target MVTR | Target RET |
|---|---|---|
| Casual rain shell | 5,000+ | <20 |
| Active outdoor | 10,000–15,000 | <13 |
| High-output / pro | 15,000–20,000+ | <6 |
Specifying Breathability as a B2B Buyer
In your brief: state both a target rating and the test method (e.g., “MVTR ≥15,000 g/m²/24h per JIS L1099 B1” or “RET ≤6 per ISO 11092”). Pair the breathability target with the waterproof rating and ventilation features (pit zips), since mechanical venting supplements fabric breathability on high-output garments.
Frequently Asked Questions
Is higher or lower MVTR better?
Higher MVTR is more breathable. MVTR measures how many grams of water vapor pass through the fabric per day, so a higher number means more sweat escapes. For active use, look for 10,000 g/m²/24h or above.
What’s the difference between MVTR and RET?
MVTR measures vapor throughput (higher is better) while RET measures resistance to vapor escaping (lower is better). RET is the lab-consistent standard preferred by technical brands; MVTR is more common on consumer hangtags but varies by test method.
What is a good RET rating for a jacket?
A RET below 6 is extremely breathable and suited to high-output activity. Below 13 is very breathable for general outdoor use. A RET above 20 indicates low breathability, suitable only for casual or low-activity wear.
Why do two jackets with the same MVTR feel different?
Because MVTR is measured by several test methods (ASTM E96, JIS L1099, sweating hotplate) that give different numbers for the same fabric. A “20,000” measured by a generous method may breathe worse than a “15,000” from a conservative one. Always compare the test method, not just the number.
Spec Breathable Shells With a Factory That Tests Them
Breathability is where comfortable jackets are won or lost — and where misleading numbers hide. Always pair a rating with its test method. At PT Outwear we manufacture custom hardshell jackets with membranes spec’d to real MVTR and RET targets, from 30-piece MOQ with 1-piece sampling. Our fabric technology team can match a membrane to your breathability and waterproof targets and supply the test data.
