Best DWR for bivy

[Jerry Adams]

I’m making a quilt/bivy

I want the outside to be waterproof enough to ward off dew and mist.

I don’t care about rain.  I use my tent in that case.  Rain is more difficult because it hits the fabric and creates a lot of pressure.  You need higher HH, like waterproof breathable (heavy) fabric.

I looked at membrane 10 0.66 oz/yd2 RSBTR and Momentum 50 0.7 oz/yd2 thru-hiker.com

Test setup – ring (masking tape), fabric over that, put in 1/2 inch of water, paper towel underneath.  1/2 inch of water is more than anything that will collect on it in real use

The membrane leaked all the water through after about 10 minutes.  It’s funny, it just sits there for a long time, then all of a sudden finds a path through, then it all leaks through pretty quickly

The momentum I bought about 2018 leaked through after a couple hours.

I also tested momentum I just bought.  It didn’t leak after a couple hours but I aborted the test because there was water from the 2018 momentum getting all over the place.  The just purchased momentum might be better, but it could just be random variation.

The momentum is significantly better – the DWR is better.  According to my crude measurement.  $13 a yard

The membrane is probably just fine.  Could be that it’s just my crude test.  $10.50 a yard.

I did the same test several years ago comparing to some other DWR nylon.  Same result.  Actually, that fabric was worse.

[Jerry Adams]

I wonder if RSBTR has a better DWR lightweight fabric

It’s all moot to me now because I’ve already purchased it and am making it.

Maybe this would be useful to someone else.

[Tuukka U]

Membrane is fairly air permeable at ~10 CFM, which makes it less likely to have a high HH. I wonder what the CFM is for the Momentum?

[Jerry Adams]

it says moderate breathability.  I suspect less than membrane

which is fine for a bivy – I want it to protect from wind

if your main concern is condensation inside, then membrane probably better?

[Michael B]

I used Membrane 15 poly ripstop on my latest quilt shell, I have some more and can do the same test you’ve done with your fabrics if you want me to.

[Jerry Adams]

sure!  that would be interesting

community effort here

and maybe some more knowledgeable person would say something

[Michael B]

test started

edit, nearly 1hr later, no change.

[Michael B]

Over 12hr later

[Jerry Adams]

Hmmm… membrane poly is 0.9 oz/yd2

That actually might be better to have the outer layer slightly heavier, sturdier

My current M50 bivy has some mouse holes in it.  Not to worry, a little Seam Grip fixed it.

[Michael B]

Yes, it is a little heavier, but I think it was a good choice for me for my quilt shell. Still produced a 19oz quilt that is good down to 30F. I like that I don’t need to worry much about being very delicate with it.

[Michael B]

I stopped the test this morning. No water went through the Membrane 15. I suspect if you need better water resistance for your splash bivvy, you are probably in a bad spot.

[Jerry Adams]

Yeah

There are times some water will puddle on my bivy for a while.  This test should cover that

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