Airtight bivy??

[jblam]

Last year I went on a few day backpacking hunt and took a bivy to save on weight I couldn’t spare elsewhere. I ended up getting caught in a ~13 hour punishing rain storm one night, not ideal in a bivy. About 3 hours into the storm I woke up short of breath and my heart rate was like 110, not my normal resting rate of 50ish. I opened the zipper a bit, stuck my mouth to the opening, and a minute or two of breathing later my heart rate dropped and I closed up shop and went back to bed. This process continued a few times throughout the storm.

While I was laying there wondering if I should have packed a snorkel for the trip, I was wondering if the completely soaked bivy effectively became air tight because it was completely water logged. Has anyone else had this happen? Opening the bivy and getting air moving fixed my heart rate every time I woke up. It did not help the 2” of water at the feet of my bivy, but that’s just luck of the draw I guess.

Oh and as a side note this was a bivy I’ve used once and is a very commonly used/highly recommended brand.

 

[tater]

I remember this from a few years back...

https://www.cnn.com/2024/11/06/us/north-carolina-wilderness-camp-death

 

[Macintosh]

I was wondering if the completely soaked bivy effectively became air tight because it was completely water logged

Yes, 100%, waterproof/breatheable fabrics cannot breathe at all if the fabric is saturated. The dwr is an integral part of the fabrics ability to breathe because it prevents the fabric from saturating (if it works).
Most bivis Ive used have a mesh “overlap” to get air without allowing water to get inside too much. And there is a learning curve to a degree. But really a bivi sack in a storm like that is survival-mode imo, it isnt ever going to be “comfortable”. Most of the bivis I see people talking about on this site are designed to be used under a tarp or some other sort of minimal shelter, not by themselves in weather like that.

 

[ozyclint]

Yep, you can have waterproof or breathable, not both.
Even to breathe you need a difference in humidity on either side of the fabric.
You can't push water vapour through a fabric into air that is saturated with humidity. Which is what happens when it rains

 

[danhuntingmi]

Scary. While I've done what you did a few times, I now use a tarp that weighs 8 oz and folds up into a quart size bag so I can keep my head completely out of the bivvy.

Borah Gear: Ultralight Silpoly Tarps

borahgear.com

 

[rclouse79]

That sounds horrible. I would opt to get a little rain on my face so I could breathe. I gave up the bivy dream due to condensation problems. Waking up damp on a clear night is annoying.

 

[Poser]

I bivied out one night while elk hunting to save time getting going to the next morning. It unexpectedly ended up snowing -heavy, wet, sticky snow which built up on my bivy sack pretty quickly. I had it zipped up except for about 6 inches and my sleeping bag ended up getting soaked with condensation. This all happened inside of 90 minutes and made for a miserable, sleepless night.

 

[jblam]

Yea, it was definitely survival mode at that point. Was a classic example of being tired and just half assing camp setup because it was just for the night.

I love going as light as possible, but dam a tent solves a lot of problems, and turns out saving some ounces on skipping a tent is a moot point when you add a few pounds of water weight to completely soaked gear.

 

[Beendare]

Yea, it was definitely survival mode at that point. Was a classic example of being tired and just half assing camp setup because it was just for the night.

I love going as light as possible, but dam a tent solves a lot of problems, and turns out saving some ounces on skipping a tent is a moot point when you add a few pounds of water weight to completely soaked gear.

You answered your own question- nice. Bivy's aren't the best backcountry option, IMO, a UL Tent is.

 

[danhuntingmi]

That sounds horrible. I would opt to get a little rain on my face so I could breathe. I gave up the bivy dream due to condensation problems. Waking up damp on a clear night is annoying.

The issue with many/most designs with keeping it open without a tarp is that water will run inside the bivvy liner.

I've used a bivvy with a tarp extensively and it works quite well while being lighter and, especially, more packable than a tent. I also consider them safer than a super light tent due to robustness and redundancy. I personally wouldn't even consider using a tent if I'm packing it any distance except maybe in some sort of extreme winter weather. Even then, probably not.

 

[rclouse79]

The issue with many/most designs with keeping it open without a tarp is that water will run inside the bivvy liner.

I've used a bivvy with a tarp extensively and it works quite well while being lighter and, especially, more packable than a tent. I also consider them safer than a super light tent due to robustness and redundancy. I personally wouldn't even consider using a tent if I'm packing it any distance except maybe in some sort of extreme winter weather. Even then, probably not.

Nice. I tried the tarp and bivy for a couple seasons. When I added up the weight savings vs an x-mid 1, I decided it wasn’t worth it for me.