Bivvy bag + rain = wet

[Bearbonesnorm]

After Chew mentioned on the Bivvy a month thread that his bivvy bag seemed to let water in and an experience I had last week, I got thinking ... does anyone have a bivvy bag that actually beads water on the surface?

I've got numerous bivvy bags and have tried lots of different ones but I don't recall having one that water will bead off. Obviously there's a good chance that the bag isn't leaking but condensation is forming inside ... the breathability drops as the outer becomes saturated.

Do bivvy bags have a DWR coating? Does a DWR coating overly reduce the breathability? Am I talking rubbish?

[Matt]

okay, so I had this with my Hunka, so I emailed Alpkit.

they told me to turn it inside out and fill it with water.

This I did and it didn't leak a drop.

So basically if it wets out on the outside it stops breathing as well as it can, makes sense, and the water on the inside is sweat

[griffdowg]

So basically if it wets out on the outside it stops breathing as well as it can, makes sense, and the water on the inside is sweat

that makes a lot of sense.

You could always coat the outside with Nikwax TX direct (spray) or their tent version. That would allow it to bead. They say it does not affect breathability, but hmmmm... Im not sure.

I suppose thats the trade off of bivi vs. tent though isn't it! be prepared to get wet to save 500-700g!

[Bearbonesnorm]

okay, so I had this with my Hunka, so I emailed Alpkit.

they told me to turn it inside out and fill it with water.

This I did and it didn't leak a drop.

So basically if it wets out on the outside it stops breathing as well as it can, makes sense, and the water on the inside is sweat

That's exactly what I thought but surely a DWR coating would help prevent the bag 'wetting out' in the first place?

[Ray Young]

I read somewhere that a bivi bag needs to have a flow of air over it in order for it to breath properly. If it's wet on the outside then I think this would reduce it's breathability and the damp inside would be condensation. Would this make sense?

[Anthony]

Pretty sure both my Rab Storm and TN Moonlight both have a DWR to a degree, water certainly beads off very well to start with.

Bivvy bags must be one of the worst things though. The combination of little air flow, full body coverage, often breathing goes inside too, one side trapped to the ground, high temperature difference between inside and out....hardly makes it easy for the fabric!

I treat my bivvybag as more of a water resistant sleeping bag cover and always use a tarp. If I need to stay sheltered I'll take the tent.

[Cheeky Monkey]

I always thought they had the same DWR coatings as regular breathable cags. My old but (so far reliable) Phoenix bag beads, or used to. Like most DWR's they seems to wear off and are affected by dirt, grease etc etc.

Check the manufacturers instructions but I imagine most rejeuvenation tips for cags would work for bags. Granger's 2 in 1 cleaner and re-proofer?

Pretty much agree with Anthony. They're trying to fulfil a pretty challenging set of requirements.

[pedalhead]

I've got a Mountain Laurel Designs eVENT bivvy with cuben fiber base which does bead water on the top, as you'd expect from eVENT. I do notice some condensation on the cuben fiber base though.

[Ian]

Interesting article here: http://www.ukclimbing.com/articles/page.php?id=4556

The bit under the "DWR" heading and references to "wetting out" are particularly relevant to this thread.

[pedalhead]

That's a great article, cheers for the link