Key takeaways
- Breathability is a fabric's ability to let sweat vapor escape, keeping you dry from the inside.
- It prevents the clammy, sweaty feeling of a non-breathable layer during activity.
- It's measured by tests like MVTR (higher = more breathable) or RET (lower = more breathable).
- There's a trade-off: more waterproofing and insulation often reduce breathability.
What breathability is
Breathability is a fabric’s ability to let water vapor (sweat) pass through it and escape, keeping you dry and comfortable from the inside during activity. It’s what prevents the clammy, sweaty feeling of a non-breathable layer, and it’s crucial for waterproof-breathable shells and active wear that need to vent the moisture you generate.
How it’s measured
- MVTR (Moisture Vapor Transmission Rate) — how much vapor passes through over time; higher = more breathable.
- RET (Resistance to Evaporative heat Transfer) — lower = more breathable (less resistance).
These lab tests allow comparison, though real-world breathability also depends on conditions, fit, and ventilation features.
Hiking hard up a rainy climb, a hiker in a highly breathable shell stays drier inside than they would in a cheap non-breathable raincoat — the fabric venting their sweat vapor — and opens the pit zips to dump the extra heat the fabric alone can’t.
The trade-off
Keeping liquid water out and letting vapor out are competing demands: more waterproofing, durability, or insulation generally reduces breathability. So highly waterproof shells (high waterproof rating) can feel less breathable, and a membrane like Gore-Tex balances the two. Ventilation features help, and breathability works alongside a base layer’s wicking.
The bottom line
Breathability is how well a fabric lets your sweat vapor escape, keeping you dry from the inside — vital for shells and active wear so you don't end up clammy. It's measured by tests like MVTR (higher = better) or RET (lower = better), and it always trades off against waterproofing and warmth. The best setups pair a breathable fabric with ventilation features to manage moisture.
Frequently asked questions
What is breathability in fabrics?
Breathability is a fabric's ability to let water vapor — the sweat you produce — pass through it and escape to the outside. A breathable fabric vents that moisture so it doesn't build up inside your clothing, keeping you drier and more comfortable during activity. It's especially important in waterproof shells and active wear.
How is breathability measured?
Common metrics include MVTR (Moisture Vapor Transmission Rate), which measures how much vapor passes through a fabric over time — higher numbers mean more breathable — and RET (Resistance to Evaporative heat Transfer), where lower numbers mean more breathable (less resistance). These lab tests let you compare fabrics, though real-world breathability also depends on conditions, fit, and ventilation features like pit zips.
Why is there a trade-off between breathability and waterproofing?
Because keeping liquid water out and letting vapor out are competing demands on a membrane. Generally, the more waterproof and durable (or the more insulating) a fabric is, the harder it is for vapor to escape, so highly waterproof shells can feel less breathable. Manufacturers balance the two, and features like pit zips help dump heat and moisture that the fabric alone can't.
Sources
- Waterproof-breathable fabrics — The Mountaineers
- Fabric technology — Gore-Tex