UL Bivy Condensation

[Ben]

I recently purchased an UL bivy and after a few nights I am having issues with it. I get a large amount of condensation - enough that I have to hang my sleeping bag every morning because it's soaked.

I've left the bug screen open, used the suspension loops to raise the bivy off my face, put the sleeping pad outside of it, and faced it into the breeze to circulate air but I still get condensation.

Any thoughts on what I'm doing wrong? Any tips to help prevent this next trip?

 

[_Nick_]

What's the weather like when this is happening? Temp/humidity/dewpoint?

 

[Ben]

It's been warm days, 40s at night, dew only in depressions or near water.

 

[_Nick_]

What bivy did you decide to get? What are you using for a groundsheet? What temp rating is your sleeping bag? Lots of variables can affect condensation rates...

 

[Ben]

Hey Nick, thanks for helping me out with this. I really do appreciate it.

My complete sleep system is: Ti goat ptarmigan bivy, 15 degree marmot down bag, big Agnes q air core pad, tyvek ground sheet, all under a 6x9 tarp that's set up for maximum air flow.

Thanks again!

 

[colonel00]

I am no expert in this area at all but man, a 15 degree bag with temps in the 40's just has me sweating already. Out of curiosity, with those temps and no bugs (you left the bug screen open) what is the purpose of using the bivy? For me, I have a bivy for use when floorless in places where bugs are bad or to keep my quilt clean.

 

[FreeRange]

I have the same bivy, with a 20 degree REI sub kilo down bag, xLite Pad and use a polycro ground sheet. The first two trips I did with the Ptarmigan were in Jan and Feb of this year. One was a multi-day upland trip sleeping in a river canyon with water close by every night, it was getting down to about 25-30 at night and very windy. I slept bivy, no tarp and was fine. Humidity was low. The other trip was a two day climbing trip with the same gear in the desert but miles from any water source , 40-45 degrees at night. First night was insanely windy, was fine, second night the wind died off, I warmed up a lot in my bag and woke up to bad condensation. I was already sleeping no hood with my shoulder out of the bag, I ended up taking my bag out of the bivy because the wind was gone and I didn't feel I needed it. I never had the bivy zipped all the way up on either trip.

I sleep hot and I think my issue was getting too warm in my bag and starting to sweat, causing moisture buildup.

I think it's a lot like rain gear, if you're sitting for hours in a cold rain storm, internal condensation won't be a worry with any rain gear, hike uphill for a few hours in the same rain gear and you're going to heat up and have some condensation to deal with. Same with bivy sacks, they're made to repel external moisture sources but have a hard time dealing with moisture created within the shell so minimize that moisture.

I'd look at how warm you're getting at night, a lot of people say a bivy can add 10 degrees to your bag rating, you already have a 15 degree bag, it's 40 degrees out, how hot are you getting in your bag?

 

[_Nick_]

I sleep hot and I think my issue was getting too warm in my bag and starting to sweat, causing moisture buildup.

This was my main thought. You're probably over-insulated for your conditions given the gear you've got. That condensation in your bag could be both sweat and condensation from evaporated sweat, driven by the fact that you're too hot at night. In conditions you mention, I often run my 50* quilt in my bivy with my Xtherm, for comparison.

So, I'd try sleeping with your quilt off to one side or something if it's going to be in the mid 40s and you don't have a lighter weight bag. See if that helps any.

 

[Ben]

Thanks for the replies. I got the bivy mainly for bugs, in case rain comes in because my tarp is pretty small, and to keep my bag clean. I have been sleeping my sleeping bag unzipped, but I will try to unzip it all the way and see if that helps.

I opened the bug screen in an attempt to allow for more circulation.

I tend to sleep cold, and have yet to feel hot or sweaty at night in the bivy with the bag zipped up all the way. Although my bag is rated for 15, 30 would be pushing it.

I'll also try sleeping without the bivy during this next trip. My only worry is that when I slept in the bivy with the bug screen open I had something crawl on my face...

 

[_Nick_]

Thanks for the replies. I got the bivy mainly for bugs, in case rain comes in because my tarp is pretty small, and to keep my bag clean. I have been sleeping my sleeping bag unzipped, but I will try to unzip it all the way and see if that helps.

I opened the bug screen in an attempt to allow for more circulation.

I tend to sleep cold, and have yet to feel hot or sweaty at night in the bivy with the bag zipped up all the way. Although my bag is rated for 15, 30 would be pushing it.

I'll also try sleeping without the bivy during this next trip. My only worry is that when I slept in the bivy with the bug screen open I had something crawl on my face...

I'd really have to bet that you're getting hot at some point in the night in a 15* bag with a bivy when it's in the 40s. You might not necessarily wake up hot or sweaty, but you might be getting that way earlier in your sleep cycles and not know it as you sleep right through it. You then wake up feeling a bit cold/wet because the sweat evaporated and re-condensed. I really have to think that's the problem.

As to critters on the face, just open your mouth and wait until they crawl to the edge of your lips. A quick swipe of the tongue and a crunch of the teeth and you've got yourself a protein rich midnight snack .

 

[Ben]

I'd really have to bet that you're getting hot at some point in the night in a 15* bag with a bivy when it's in the 40s. You might not necessarily wake up hot or sweaty, but you might be getting that way earlier in your sleep cycles and not know it as you sleep right through it. You then wake up feeling a bit cold/wet because the sweat evaporated and re-condensed. I really have to think that's the problem.

As to critters on the face, just open your mouth and wait until they crawl to the edge of your lips. A quick swipe of the tongue and a crunch of the teeth and you've got yourself a protein rich midnight snack .

Haha, thanks again for the help! I'll be sure to leave the bag open to keep cool.

 

[Ben]

Ok, update time....

I left my sleeping completely unzipped and only covered about half my body. Before I went to sleep I would describe my temperature as 'cool'. However, I still woke up with my bag soaked. Most of the condensation is between the top of the bag and the top inside of the bivy. Every morning I had to hang my bag up to dry and some days it took to noon to completely dry out.

Any other ideas as to why this may be happening?

 

[Violent Hippie]

I have used heavy duty bivies such as integral designs and kelty brands by simply laying on the ground fully zipped up with no tarp on the ground or over me and never had a condensation issue over approximately 50 nights of use. I am not sure what is going on there especially if you had in unzipped besides the previous mentioned theory of you possibly sweating inside the bag ? I have not used an UL bivy but have been planning on buying a borah most likely. I have not heard of this occurring to others so I hope you get it sorted out.

 

[Riverwalker]

The warm air coming through your bag hits the cool inside or outside of your bivy poof condensation, it's science!

 

[_Nick_]

Man I don't really know what to tell you. Is it possible that your bivy is too big? If there is a ton of space between your bag and your bivy then that could allow the chilled air to more easily get into your bivy causing condensation.

 

[fillthefreezer]

i get the same thing maybe 50% of the time. typically when humidity is high. if its windy, no condensation. i dont have an answer. my partner does not have same issues although hes had condensation a few times.