Bivy experts: condensation issues in light splash bivy

I wouldn’t call myself a bivy expert, but I’d say what you experienced is pretty standard. Some folks have added a strip of no-see-um down the center top of their bivy to increase ventilation, and you end up with something like the MLD BB2. IMO, this is the way with bivies – Otherwise, just not the right tool for the job.

What were the weather conditions during your tests? Were you sleeping under a tarp, or under the night sky? The latter will lead to increased condensation, all other things equal. Try pitching under a tarp if you encounter the same conditions (which, unfortunately, are theoretically ideal times to use just a bivy right??).

That’s all I got. I’m sure other, real experts will chime in :)

@ Phong

As Erik says, any piece of kit has its limitations.

Did you have the zipper all the way zipped up? You might try venting next time. Otherwise there is no place for the water vapor from your body to go.

Also location matters.  In the instance where you were camped next to a river, I would propose that a silnylon tent probably would have experienced the same kind heavy condensation on the inside of its walls.

So I’ve been exclusively tarp/bivy for 2 years now.  I have yet to have any major condensation issues.  I use a Borah gear bivy and I think the top fabric breaths very well.  I’m not familiar with the breathability of the MLD top fabric but I own a good bit of MLD gear and it’s all top notch so I’m sure it should breath pretty well.  I know that lots of people talk about having issues with condensation inside the bag but I haven’t found that to be the case.  It’s possible that you are breathing down into the bivy throughout the night and that could be the cause.  When I’ve woken up with my face tucked down below the mesh I get a bit more condensation.  I’m curious how wet  you mean by “drenched”.  Do you have pooling water?  Is your down quilt damp to the point that it has lost all loft?  You’re going to have a little moisture always but I haven’t ever had a situation where I felt like I needed to dry out any gear.  As Erik G said above, use a tarp to block cool breezes and maybe try tying up the head end to get some more circulation.  My hunch is though that you were probably used a toasty warm 20 degree bag and insulated sleeping pad, and maybe were wearing alot of insulation as well.  You probably curled up nice and toasty warm in your bivy, and while you slept your body pumped out a ton of moisture and you woke up dripping in it.  Maybe try using less insulation and layering?  Just enough so that you’re not cold.  Regardless, after some trial and error you’ll likely find a sweet spot.  Good luck!

Hrm…so to clarify…I guess drenched was too strong a word.  There was coldness and some moisture in between the bivy bag and the top of my quilt.  At no point did the moisture get into my down or effect the loft.  So I think I thought it was a lot of condensation to me, because I’m not used to that moisture on my bag.  It dried off in about 15 minutes without any wiping or flapping.  I world characterize it as the same kind of condensation that appears on your tarp surface in the morning of a typical night.

My tests were all carried out under the open sky.  I’m starting to think that this is pretty normal.  It didn’t affect my warmth at all.  I was concerned about build up of moisture with day after day of condensation and no sun to dry off.  But if that were to happen, then maybe i’d just get under my doumid anyway, so perhaps this will work out for me after all.

What I’m hoping to achieve is the ability to camp under the sky most of my trip.  I want to only use my mid if its really cold/wet/windy.  So under nice conditions, a little condensation would probably dry up during the day so I’ll be set for the next day anyway.

Glad I talked to you guys!  Lol.

@ Phong

Sounds like you are golden then. I must say I use my MLD bivy in combination with my MLD synthetic quilt several times a season under the stars in the Sierra during the summer and in the Santa Cruz mountains in other seasons and have not experienced the kind of condensation issues reported in other threads. I do often leave the zipper open when there is no wind and sometimes I even find myself sleeping on top of the bivy. When there is a threat of rain, I pitch the tarp close by but start the night under the stars.

Cheers

I’ve had that experience when its 25F, under a clear sky.

Due to radiation, the outer layer of the bivy cools another 10F or so.  Then, water vapor from my body goes out through quilt, hits the inside of the outer layer of the bivy, and freezes.

When I slept under a tarp or trees it was okay.

Same thing with me, the water didn’t get into the quilt, and dried out in the sun the next day

You issue is definitely the clear sky with no cover to stop the radiation, worse near water and temps near freezing.  Here is my piece on bivy condensation.

I believe I read your article a few years back Alex, when I was looking to make the switch.  After a couple of years in the bag, I can say your info is spot on from my experiences.  Thanks for linking it back here.

If you had no bivy, the condensation (dew point) would be occurring inside of the sleeping bag shell where you wouldn’t notice, most likely.

Alex that’s a really good article on fabrics. I wonder if it’s the DWR coating that causes modern fabrics to condense more.  If I were to MYOG a bivy, any recommendations as to what a good top fabric would be?  I would still like to keep it ultralight.  7 ounces or so.

Phong it is more the slickness of the inner face, don’t know which of the light fabrics would have a more wicking surface.  That is why many folks go with some mesh down the center

I have used all of my bivies in various weather/conditions and seasons over the last 10 years or so and have yet to have any condensation problems of any real concern. Thats not to say I have never had condensation.. just not much to the point where I noticed it or was worried about it. In fact, I have noticed more condensation when using a single wall tent then when using my bivies.  Sometimes I set it up with the mesh pulled off my face, sometimes not.. it all really depends if I have time.. meaning.. if i am throwing my bivy down to sleep in in.. then no need to pull mesh off my face.. If I am setting it up and have time, hang around camp, lay and relax for a while.. then I pull it up off my face. Sometimes I pitch a tarp overhead.. Sometimes not.. all weather dependent.

Bivies I use are: Borah Gear Bug bivy, Borah Gear Snowyside Event bivy, Katabatic Gear Bristlecone bivy and I just picked up a Katabatic Gear Pinòn bivy.

100% satisfied and love using them all.