BMW Vapor Bivy Condensation

[Bob Gabbart]

Over the weekend I used the BMW Vapor Bivy and when I woke up in the morning, there was significant condensation on the silnylon which got the edge of the down sleeping bag wet. So my question is: Why did this happen and what can I do to prevent it?

Here is the situation: The bivy was under a small tarp. It was about 48 degrees and humid. I slept with the bug netting zipped in and the top of the bivy was NOT tied to the tarp. My guess is that the condensation was because of a lack of ventilation within the bivy since the netting was zipped in. Would tying the bivy to the tarp to raise the hood increase ventilation and fix this problem?

Thanks,
Bob

[Dane Burke]

Unfortunately, I have only been able to spend two nights in my vapr bivy. The first night was in lowlands surrounded by trees and under a poncho tarp, with a little rain. The head end of the bivy was suspended from the tarp, with the netting zipped in. The bivy couldn’t have performed better. The second night was right on top of a peak (with the full moon, mountain silhouttes, and view of Seattle, I couldn’t resist). I couldn’t find a place to pitch my tarp because it was so rocky, so I used the bivy as my only shelter. It was windy but did not rain. I tried tying the hood up to a shrub but eventually took it down. After about 5 hours I had really bad condensation between the sleeping bag and the pertex of the bivy. The outside of the bivy was dry and so was the inside of the sleeping bag, but the top half of the down was really wet and clumpy, not just damp.

I think the only differences between the first night with perfect performance and the second night with condensation was not suspending the hood, not sleeping under a tarp, and being on a windy peak rather than a sheltered forest.

I really doubt the wind would cause condensation rather than carry away moisture, and Bob had a similar problem while using a tarp, which makes me think it was the hood not being suspending which causes the condensation.

Has anyone else had this problem, or have a better idea of what is causing it?

[Ryan Jordan]

I’m not surprised at all with your condensation experience.

I’ve experienced it on numerous occasions.

I don’t have to deal with extreme humidity here in the Rockies, but you get this when the temperature hovers around freezing (25-35) and you have the bivy zipped up. I see it most when I roll to my side and thus do not breathe directly out the top of the bivy.

I don’t know that there is a remedy, except for me, when it was that cold, I knew the mosquitoes wouldn’t really be a problem, so the netting stayed open. Conversely, closing that netting window does retain some heat which is a nice feeling when your sleep system is a little on the thin side!

Condensation is always a bugger to manage, and remains a reason to seriously consider synthetic bags if you’re out for long trips with no opportunities to dry out, as you might be doing with high mileage days or in bad weather.

[Bob Gabbart]

Ryan,

You didn’t address the option of tying the hood to the tarp to increase ventilation. Have you found that this helps?

Thanks,
Bob

[Ryan Jordan]

Yes, it helps a lot. You can even overwhelm the breathability of the quantum and get condensation on the quantum top if the hood is not lifted and it’s cold and/or humid and you are breathing in the closed bivy.

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