Condensation in a Jacket
Condensation is moisture from your own body turning back to liquid on the cool inner surface of a shell. It is the most common thing mistaken for a leak.
It happens when you produce vapour faster than the fabric can pass it, or when the outer face has wetted out and stopped breathing. The jacket is working; it simply cannot keep up.
How to tell it from a leak
| Condensation | Leak | |
|---|---|---|
| Where | Even, across chest and back | Patchy, at seams, zips, shoulders, hood |
| When | Worse the harder you worked | Worse the longer it rained |
| Outer face | Water still beads, or has wetted out | Often still beading |
| Fix | Ventilate, slow down, reproof | Check seam tape and zips |
What actually reduces it
Mechanical ventilation, first and by a distance: pit zips, a two-way front zip opened from the hem, open cuffs. Then effort management, since the vapour you do not produce does not need removing. Then keeping the DWR intact so the face fabric does not wet out.
A higher breathability rating helps least of the four, which is the opposite of what most product marketing implies. See pit zips.
Where it is unavoidable
Hot humid air, where there is almost no vapour pressure gradient for the fabric to work with, and any sustained hard effort in a waterproof layer. In those conditions you will be damp inside whatever you are wearing, and the only real choice is how well you can vent.
Related terms
- Wet-out: the other half of the problem
- Waterproof and breathability ratings explained: why the rating helps less than expected
- Pit zips: the fix that actually works
- Glossary: all terms