I'm used to think of monolithic PU membranes as (barely) breathable stuff while the coatings render the fabrics just plain waterproof, non-breathable, is this technically correct?

PU membranes work (in the breathing side) by a differential in humidity if I remember right and the breathability depends heavily on how thin the membrane is. Do coatings work the same, even if it's marginally? And if not, why not? Something about the difference between laminating a film and coating fibers? something else? is the PU in a membrane the same as the one used for coatings or is PU (as we know it for outdoor apparel use) just a generic term for something that can take different shapes / properties?

Goretex (and many other brands) incorporate a wp/b membrane plus a PU layer that may be laminated or coated on. This PU layer does not render a garment non-breathable -- it can still breathe -- but the breathability is, of course, compromised to a degree.

The higher the differential in temp and humidity between the inside and outside of the garment, the better the garment "breathes". So a wp/b garment performs the best in cold and dry alpine environments -- and it performs not at all in warm/humid climes.

eVent is the newer technology. The eVent laminate makes a garment rainproof -- without need for that additional PU layer. Breathability is significantly higher at a wider temp / humidity range.

Of course, there is no miracle fabric out there. If you think about it, you can work up a sweat wearing the thinnest tee shirt hiking up a mountain slope. But in terms of keeping you dry longer in a wider temp/humidity range -- skip Goretex and the myriad of laminates/coatings that incorporate PU -- and go for one of the following that maintains waterproofness without a PU layer:

1. eVent
2. MontBell's Breeze Dry Tec
3. Driducks

Edited by ben2world on 09/07/2010 10:41:18 MDT.

I'm aware of all the stuff about Gore-tex, eVent and PU laminates (basically through those old BPL articles) but what I wonder now is about PU itself. Like a traditional, PU coated tent fly, is it any different from a PU laminated jacket other being coated instead of laminated or possibly the thickness of the PU layer? anything else?

My guess is that the PU laminate (or coating) on a garment is much thinner than on a tent fabric -- to allow for a sufficient degree of waterproofness -- while still allowing for some water vapor (sweat) to escape. Also, a jacket is not stretched taut and exposed directly to the sky for hours and days -- like a tent might be.

But for me, I don't really care. Why? Because there are now at least three options (as listed above) that provide waterproofness without the need for that layer of PU laminate or coating at all.

Edited by ben2world on 09/07/2010 11:03:53 MDT.

I know the options but I'm just curious. It's still a relevant question as most of the WP/B market, as far as I know, is still PU technology. Which leads me to another question I'm curious about, why is that? is WP, direct venting technology only known to eVent and Montbell, is it a patent thing?

I came across one called Dintex. Looks to be something similar to Gore Tex, though the options for it look to have some with and without an added membrane.

Interesting stuff, wonder if any of you have seen it?