Wet Weather Breathability

I remember my first waterproof breathable jacket. I can’t remember if I received it for Christmas or my birthday, but whichever, it was expensive and I felt especially lucky to get it. That is close to 25 years ago now.

I also remember the utter disappointment of getting wet in it for the first time!

It took quite some time to figure out why. The problem isn’t so much that rain can get in, it’s that condensation can’t get out.

What’s the most breathable fabric you can think of? How about a spider’s web? I’m sure everyone has seen dew (condensation) on a web… this shows that if the fabric is cold enough, it will get condensation on it, regardless of how breathable it is.

When it rains conditions are often cooler and water running over your waterproofs has a powerful chilling effect. That’s why water is used to cool engines: it has a high heat capacity, high conductance and absorbs massive amounts of energy to evaporate. Once the outer fabric of a jacket becomes saturated, (perhaps because the water repellency has worn off or because condensation has occurred within the fabric) then the waterproof membrane becomes chilled. Once it’s cold enough, (the dew point temperature) condensation occurs.

Making waterproofs breathe in the wet is what we have set out to do!