| What it is | Letting sweat vapor escape |
| Counterpart to | Waterproofing |
| Measured by | MVTR (higher = better) or RET (lower = better) |
| Matters for | High-output activities |
Breathability is a fabric’s ability to let water vapor (sweat) pass from the inside to the outside, keeping you dry from perspiration. In waterproof-breathable gear it’s the counterpart to waterproofing, and it’s measured by ratings such as MVTR (g/m²/24h) or RET (resistance — lower is more breathable). High breathability matters most for high-output activities.
Paired with waterproofing
Read it alongside the waterproof rating; a failing DWR kills breathability. Membranes like Gore-Tex and eVent balance both.
Frequently asked questions
What is breathability in a jacket?
Breathability is how well a fabric lets the water vapor from your sweat escape to the outside, instead of trapping it and leaving you clammy. In a waterproof-breathable jacket, breathability works alongside the waterproof membrane so you stay dry from rain outside and perspiration inside.
How is breathability measured?
Two common metrics: MVTR (Moisture Vapor Transmission Rate), in grams of vapor per square meter per 24 hours, where higher numbers mean more breathable; and RET (Resistance to Evaporative heat Transfer), where lower numbers mean more breathable. Test methods vary, so compare figures from the same method.
Why isn't my waterproof jacket breathing?
Often the face fabric has 'wetted out' — its DWR has worn off, so water soaks the outer layer and blocks vapor from leaving the membrane, making you feel damp even without a leak. High exertion can also outpace any membrane. Restoring the DWR and using pit zips for ventilation help.
Sources
- Breathability metrics — The Mountaineers
- Fabric performance — W. L. Gore & Associates