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Extreme but effective condensation prevention in a bivy or single wall shelter?
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John Nestler
(nessles) - F
real life bivy breathing mask on 07/28/2012 17:49:38 MDT Print View

I've been looking for a solution for condensation as well as emergency situations to seal up a bivy during a rainstorm. Using a light 3M respirator and some vinyl tubing I built a "Bivy Breathing Mask." It's quite comfortable although it seems rather bulky to bring on a trip, but it could save bringing along a tarp.

Bivy breathing mask

Read more about the "Bivy Breathing Mask" and go here for directions:

This is my first post in the forums, and I'm sure I'll find a lot of interesting advice and projects here in the future.

See you guys around!

- Nessles

Edited by nessles on 07/28/2012 17:52:02 MDT.

David Thomas
(DavidinKenai) - MLife

Locale: North Woods. Far North.
Re: real life bivy breathing mask on 07/28/2012 18:51:29 MDT Print View

As a HX, mass-flow, psychometric weenie (Chemical Engineering / Berkeley), I have a number of thoughts.

1) absolutely, this will reduce condensation in your bivy,
2) it may take a while to adjust to sleeping with the mask on, but users of CPAP machines (my wife is an MD boarded in, among other fields, sleep medicine) have to deal with much more and they adjust.
3) you definitely took the right approach by using check valves close to one's face. You could share the tubing to reduce weight/bulk, but shared (in = out) tubing inceases the "tidal volume" and while reducing condensation in the bivy just as much, it would increase your uptake of CO2.
4) the reduced CO2 in the bivy may be the biggest benefit. I find I react (unfavorably) to the CO2 when I tuck my head inside my sleeping bag then I do to the humidity build-up.
5) the vinyl tubing you used is cheap and widely available. But HPDE tubing (as used in a radiant slap floor) is tougher and slightly lighter in the same diameter. Readily available in 100- to 300-foot rolls, Home Depot will sell it by the foot. There's 1/2", 5/8" and 3/4" available for residential appilcations and larger sizes for commercial use.
6) the length of tubing is a trade-off. Shorter is obviously lighter and offers less restricted flow. But longer gives you more flexibility in sleeping positions.
7) I strongly recommend you wrap some duct tape around your water bottle so you have some repair supplies handy. Even better is the 2" wide, red plastic tape used to seal vapor barriers in homes - it is stickier, stronger, and lasts for years instead of months.
8) **advanced concept** if you consider a tube-in-tube configuration for greater heat exchange or reduced number of tubes, here's the punchline: for X diameter in the inner tubing, you'll get equivalent pressure drop in a length of 2X diameter for the outer tube. e.g. if 5/8" ID works, you'll need 1-1/4" ID for the outer tubing with 5/8" inside of it. That seems really big with a lot more cross section but it is because of the increased "wetted area" of all those tubing sides exposed to the air flow. Probably better to tape two 5/8" diameters together an forego the HX. Maybe with a stick or lightweight plate taped to the end so it stays outside the bivy
8.1) There are HX masks with two check valves built in sold for aspiring avalanche victims so they can breath in and out of a chest-worn diffuser even when buried in snow. You've achieved something similar at a lower cost and weight, but you might look at those units for inspiration and/or parts. For high-altitude work, I like the how such a rig can capture heat from out-going breath and potentially recapture some moisture as well.

James Klein

Locale: Southeast
Re: Re: real life bivy breathing mask on 07/28/2012 20:54:29 MDT Print View

Neat thread, and nice manifestation of the idea John. Thanks for posting.

I have considered making something like this before, this is nicer than what I was putting together in my head...:)

One thing I have used in a similar vein is, dust mask with light fleece pulled over. It took a few tries to find a dust mask comfortable enough for sleeping and I had to punch holes in it b/c I felt like I wasn't getting enough air. The fleece helps hold it in place and acts like a little HTX and captures some of my exhauled moister.

I have wondered if fleece would be more effective directly over my mouth and nose.

Jim Colten
(jcolten) - M

Locale: MN
Re: real life bivy breathing mask on 07/28/2012 21:34:22 MDT Print View

interesting project.

I wonder how it'd work for piping exhaled air away from a sleeping bag or balaclava to reduce frost buildup near the breathing hole. Also taking intake air from inside the bag/quilt?

eric chan
(bearbreeder) - F
ninja on 07/29/2012 09:21:03 MDT Print View

the UL way of course is to use reed tubes found by the rivers ... ninjas use em to hide underwater ;)

of course with that mask you can hide from bears in the river ... or from polar bears under the snow =O

John Nestler
(nessles) - F
thoughts.. on 07/30/2012 10:40:30 MDT Print View

David - Thanks for the insight. The mask will significantly reduce condensation inside the bivy as well as it fits well. I like the idea about inserting one tube inside the other. That would certainly warm the air as it enters the mask while cutting down on bulk - could be a good project for someone to continue on. Good idea on the vapor barrier tape too.

James - Glad you like it!

Jim - Of course you could position the intake tubing inside the bag to pull in heated air and exhale it outside of the bag provided that the input air source doesn't run out!

I'll post it somewhere else, but I use the Marmot Alpinist Bivy and it doesn't have any tabs to hang it from tree branches. Is there an easy way to make a little apex by hanging the fabric ontop so that it doesn't com into contact with the sleeping bag. Perhaps a washer and a line?

- John

David Olsen

Locale: Steptoe Butte
Heat loss in breath on 07/30/2012 11:05:46 MDT Print View

The heat from breath should somehow be trapped in the sleeping system, not just released
to the outside. Same with moisture from breath. Think "DUNE".

Larry De La Briandais
(Hitech) - F

Locale: SF Bay Area
Lighter weight mask on 08/01/2012 16:10:38 MDT Print View

For a lighter weight mask you could look into using the masks they use for CPAP machines. They only cover your nose so you have to train yourself to sleep with your mouth closed. I wouldn't think one could, but CPAP users everywhere do. It wasn't hard for my wife and she has slept for "many" years with her mouth open. Basically the have a big band that holds you mouth closed. You wear that for a week or so and you are magically trained.

Thomas Rayl
(trayl) - MLife

Locale: SE Tx
Anti-condensation snorkel on 10/22/2013 12:10:13 MDT Print View

Greetings all... I just stumbled across this thread and -- though it's a year old at the latest post -- I had some thoughts if anyone's still interested. Here's my thoughts:

The basic function of the apparatus seems to be to (1) reduce condensation by getting exhalation air "out of the arena", (2) ensure an adequate supply of breathable (ie, non-rebreathing) air when "zipped in" to a bivy, sleeping bag, or whatever, and (3) pre-warm inhalation air.

Tube-within-tube systems sound great at the start, but become much more complex when you consider the issue of keeping the inner tube CENTERED within the outer tube. Otherwise, you get more kinky airflow and lose some of your head exchange. I propose a different approach:

I would consider a two-separate-tube system, one for intake and one for exhaust, each with the appropriate one-way valve, of course. Obviously, the exhaust tube ends up "outside" the tent/bivy/bag, or whatever to ensure the exhaust moisture is effectively removed from the anti-condensation area.

It would seem viable to have the intake end of the input tube tucked toward the bottom of the sleeping bag. (I conceptually envision it rubber-banded to an ankle.) This would draw in warmed air from inside the sleeping bag. Yes, that air would have to be replaced by unheated air from "outside" somewhere, but I would think there would be a pretty even trade of heat "lost" due to the influx of outside air into the bag (to replace the inhaled air) and head "gained" due to breathing in already-warmed air. The added benefit: you are automatically pumping moisture evaporated from the body which would otherwise collect in the bag insulation or go through it and condense in the bivy/tent out via the lungs and exhaust tube. Hopefully, that would keep things significantly dryer.

(Yes, one would have to exercise due diligence regarding issues of flatulence. 32 nudge-nudge-wink-wink comments elided here...)

I had originally thought that the exhaust tube (but not the intake tube) could be a super-light-weight tube of fabric (silnylon or some such), but the outside end may tend to freeze shut for those who like to camp with showflies instead of mosquitoes.

So, anyone have any thoughts?

icefest From Australia
Mouthpiece on 11/10/2013 03:45:34 MST Print View

If you are considering using lightweight materials, consider trying to get in touch with an anaesthetist and getting some used anaesthetic machine air lines. Or you can buy them here:
They also can be extended to several feet in length.

Anyway, they'd be the lightest around and in combination with a nose clip and a lightweight snorkel mouthpiece you be looking at less than 1/2 a pound for the entire setup.

Air line with Y splitter

Hikin' Jim
(hikin_jim) - MLife

Locale: Orange County, CA, USA
Re: Reducing Condensation in a bivy on 11/12/2013 10:50:20 MST Print View

Interesting idea with tubes and such. Seems a little hard to get used to, but I guess CPAP users do it all the time.

On a slightly different note, I've tried a Polar Wrap hood that I bought at Sierra Trading Post. Kinda heavy, but I really wanted to reduce condensation inside my shelter.

My results weren't all that encouraging. The inside of my Gatewood Cape still had condensation on it in the morning. I didn't have any way to compare to how it would have been without the Polar Wrap, but the Polar Wrap certainly didn't entirely eliminate the condensation. Note: It was very damp then night I camped out, having rained the day before.

I also noticed that the Polar Wrap itself got a little damp which seemed a little unpleasant although not horrible. I haven't experimented with it more since last winter. Maybe I'll take it out again now that it's cooling down here.

Adventures In Stoving

icefest From Australia
polar wrap on 11/12/2013 13:27:34 MST Print View

Where were you expecting the condensation to go with the polar wrap?

From the looks of it, it just warns up the site you breathe in, there is no condensation removal.

Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: real life bivy breathing mask on 11/12/2013 13:37:33 MST Print View

Yeah, well, a snorkel might carry your breath out, but your body will still be evaporating. Your bivy bag will not stay dry in bad conditions.


Roger Caffin
(rcaffin) - BPL Staff - MLife

Locale: Wollemi & Kosciusko NPs, Europe
Re: Re: Re: Extreme but effective condensation prevention in a bivy or single wall shelter? on 11/12/2013 13:41:23 MST Print View

"A classic problem with sleeping in your tent in brutally cold conditions is waking up to find the inside of the tent lined with frost. Highly breathable fabrics will only go so far towards solving this problem. Even a tent made entirely out of mesh would still be lined with frost in the morning! To deal with this issue, NEMO created the Condensation Curtain™ to partition the area in which you breathe. The curtain attaches to the walls and ceiling of the tent and lightly drapes over your body around the chest area, trapping most of the vapor from your breathing in a small portion of the tent. In the morning, you simply pull the curtain aside and get dressed in the dry area of the tent! The Condensation Curtain™ is easily removed, shaken out and replaced."

Hysterical. Maybe the designer has never slept in the snow?

Reality: 'trapping most of the vapor from your breathing in a small portion of the tent' so you wake up with either condensation from the Curtain, or frost crystals, dripping all over you and your quilt/SB. Frankly, I suspect you would end up wetter with this thing than without.


Hikin' Jim
(hikin_jim) - MLife

Locale: Orange County, CA, USA
Re: polar wrap on 11/13/2013 10:53:22 MST Print View

> Where were you expecting the condensation to go with the polar wrap?
Several people on several different forums mentioned the idea that a heat exchanger type mask might help alleviate condensation. Sierra Trading Post is cheap. I thought it might be worth a try. Didn't seem to help much. I certainly can't articulate a mechanism by which it would work.

> From the looks of it, it just warns up the site you breathe in, there is no condensation removal.
Yep, pretty much. Maybe it helps prevent bitingly cold air from going into the lungs. Again, it didn't prevent condensation.

Adventures In Stoving