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How to Sleep in a Bivy w/o Dying?
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Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
How to Sleep in a Bivy w/o Dying? on 12/08/2007 16:18:50 MST Print View

Okay, a slightly dramatic and silly title for a post but I am hoping to get some advice on sleeping in a bivy.

I recently ordered a MLD Soul Side Zip Bivy with the eVent top and a MLD Silnylon Poncho Tarp.

This will be the first bivy that I have owned and used.

I am trying to transition from using a Contrail Tarptent to a Bivy/Poncho Tarp.

I notice the following disclosure and warning on MLD's website:

NOTE: Complete head enclosure in any bivy sack is not recommended. Proper instruction is required and is not provided by MLD.

So my question is:

How do you sleep in a completely enclosed/zippered up Bivy without suffocating yourself?

I ask because I could see a situation where I am in the bivy without a tarp and it suddenly starts raining. It might be necessary to zip up the entire bivy to keep the rain from coming in.

Any information would be appreciated.



Christopher Plesko
(Pivvay) - F

Locale: Rocky Mountains
how to not die in a bivy on 12/08/2007 18:44:05 MST Print View

turn upside down and breath out a small opening ;)

No one said bivying without a tarp is all roses. Haha.

Glenn Roberts
(garkjr) - F

Locale: Southwestern Ohio
No reason to die in a bivy on 12/08/2007 20:46:56 MST Print View

" a situation where I'm in a bivy without a tarp..."

Why would you be in that situation? When I use a bivy, the tarp automatically goes along. If the weather is at all dubious, the tarp gets pitched. I might still put the bivy outside the tarp for some stargazing, but when it starts to cloud up or rain, it only takes a few seconds to drag it under the tarp.

Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
No reason to die in a bivy on 12/08/2007 20:53:44 MST Print View

Funny that I should have posted this today....when I got home my Bivy and Poncho were waiting for me.

Now that I have had a chance to lay it out and put my sleeping pad and sleeping back, I can see that I would just leave a small opening to let some air in.

As for why I would not pitch the tarp if it were to suddenly rain, due to my inexperience.

I have never used a tarp before.

Now that I have my Poncho/Tarp, looks like I will be spending some time getting familiar with pitching it.

I realize that my question was a bit silly in hind sight, but I am relatively new at this.

Thanks again for taking the time to reply back to me.


Roleigh Martin
(marti124) - MLife

Locale: Moderator-JohnMuirTrail Yahoo Group
Re: No reason to die in a bivy on 12/08/2007 20:57:10 MST Print View

The Tarptent Contrail is nice and provides the functionality of a tarp and a bivy, so why did you not like it? Why did you decide to switch, how much weight are you saving?

Edited by marti124 on 12/08/2007 20:58:13 MST.

(beenay25) - F

Locale: Intermountain West
Re: No reason to die in a bivy on 12/08/2007 21:31:47 MST Print View

It's not a silly question, Tony. Suppose you didn't want to pitch a tarp? Bivies are popular in mountaineering also, where a lot of the places they're used aren't suitable to pitching tarps. So apparently there are people who are using bivies in storm conditions and apparently living to tell about it. I'm also interested in how safe/unsafe it is to sleep in a bivy completely zipped up (as I am in the same boat as you in wanting to get an MLD eVent bivy for the ability to use without a tarp). I don't really feel like your original question has been answered, though. Chris pointed out that you can turn the bivy upside down but does that apply to a waterproof-breathable bivy like the eVent ones made my MLD? Isn't eVent a "breathable" fabric and shouldn't it allow carbon dioxide to diffuse out and oxygen to diffuse in before levels become lethal? I don't know...I was confused by that note on the MLD website too (though I sort of suspect it's a joke).

Edited by beenay25 on 12/08/2007 21:35:53 MST.


Locale: Pacific Northwet
Re: Re: No reason to die in a bivy on 12/08/2007 21:41:06 MST Print View

You can always use a headtent. Here is a freestanding model:

head tent

Make sure you read the description.

Edited by DanG on 12/08/2007 21:48:34 MST.

John S.
(jshann) - F
Re: Re: No reason to die in a bivy on 12/08/2007 22:16:33 MST Print View

You should never fully enclose yourself in ANY bivy. No joke.

(beenay25) - F

Locale: Intermountain West
Re: Re: Re: No reason to die in a bivy on 12/08/2007 22:19:08 MST Print View

Sounds like you know what you're talking about. Could you explain why not?

John S.
(jshann) - F
Re: Re: Re: Re: No reason to die in a bivy on 12/08/2007 22:45:40 MST Print View

All or nearly all bivy sack makers will have a warning not to fully enclose yourself in, but leave a gap of about 6 inches to prevent suffocation. You also run the risk of major condensation when breathing inside bivy sacks. Makers of sleeping bag covers not using waterproof/breathable material may not have same warning..dunno.

check product info for this bivy.

Edited by jshann on 12/08/2007 22:56:56 MST.

douglas girling
(dgirling) - F

Locale: Adirondacks
How to sleep in a bivy w/o dying on 12/09/2007 06:09:54 MST Print View


Sleeping in a fully sealed bivy sack is indeed dangerous. There are real case reports of people dying inside their bivies. Asphyxiation was assumed in these cases - (I have never seen a coroners report verifying the cause of death) but I think this is a relatively good assumption.

The reasons below may help explain why this is a bad idea, but they are conjectural, I haven't seen any good studies verifying these issues (if anyone has please let us know)

Firstly, in sub freezing temperatures the water vapour will freeze in and on the bivy material making it in essence completely air tight. Obviously this is not a good time to be fully enclosed in your bag.

Secondly, in above freezing conditions the question is, will the breathability of the particular fabric allow enough air exchange to support your respiration. For example, you could take a cotton bag or clothing, put it over your head and continue to breath just fine. Now try this with Event, Momentum, Goretex or any of the breathable materials - you have to blow and suck really hard to get air to move through the fabric, and even then you can't get enough air to survive.

Thirdly, in above freezing conditions water vapour condensing on the surface may impede breathability too. Certainly, using the above example, if you wet the cotton you will no longer be able to breath through it. It is possible a layer of condensation on the breathable fabrics will impede diffusion of air (although these fabrics are much more hydrophobic than cotton, at some point the pores are going to be saturated with vapour.)

Again this is all conjecture. It would be interesting to do some studies and monitor the actually CO2 and O2 levels in a sealed bivy. Perhaps this has been done, anyone know?


Glenn Roberts
(garkjr) - F

Locale: Southwestern Ohio
May have misunderstood you on 12/09/2007 06:41:32 MST Print View


I may have misunderstood your post about being in a bivy without a tarp. I read your original question to mean that you didn't have a tarp available; your later post makes me think you meant you had a tarp along, but hadn't pitched it. In that case, you'd throw the tarp over the bivy to keep it dry while you rigged the tarp quickly over it. Sorry for the misunderstanding.

barry hitchcock
(barryspoons) - F
bivi without dying on 12/09/2007 12:05:44 MST Print View

i have a terra nova double hooped bivi --its top material is goretex flo2 gas permeable--when using without hoops i have often had to zip myself in completely when its rained in the middle of the night--no instructions that advised not to--- in cold conditions i put in the hoops and my head is under the mesh of the " door " which slopes at 45 degrees --watching cold snow bouncing of the mesh 2 inches above your face is soporific---if i have to zip the material of the door up completely there is a small mesh covered opening above my feet for ventilation however without hoops in this would not work--i do not have a tarp so using in rain is "challenging"

(beenay25) - F

Locale: Intermountain West
Re: How to sleep in a bivy w/o dying on 12/09/2007 12:23:06 MST Print View

"Again this is all conjecture. It would be interesting to do some studies and monitor the actually CO2 and O2 levels in a sealed bivy. Perhaps this has been done, anyone know?"

Here's a simple way to test it: rig up a candle to burn inside a sealed up eVENT or Gore-tex chamber. If the candle keeps burning indefinitely, then apparently there is some diffusion of CO2 and O2 happening. Whether there's enough diffusion for a breathing human to be "safe" in a sealed up bivy would require some more sophisticated tests.

Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
Why I love this website on 12/09/2007 14:09:06 MST Print View

To answer some of the questions that came up in response to my post.

I love my Contrail Tarp tent and have no complaints.

I am hoping to use the MLD Soul Side Zip eVent top Bivy and a MLD Silnylon Poncho Tarp as a means to cut weight.

My hope is that I can use the Bivy in place of the Contrail , use the Ponhco/Tarp in place of my rain jacket, and I am hoping to be able to swap my 2 lb 3 oz. 15 Degeee Marmot Helium EQ bag with my 1 lb. 40 Marmot Atom bag to save weight.

The key is: Will the bivy provide more warmth vs. the Contrail and enhance the warmth of the sleeping system?

Optimistically, I might save up to 2 lbs with this setup.

Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
Why Would I use a bivy with the tarp on 12/09/2007 14:23:34 MST Print View

Another question that came up...why would I not use a tarp with the bivy?

In part, because I have never used a tarp before in my life, it is all new to me.

I figured that if I completely screw things up, I would have just have the bivy to protect me. Hence why I opted for the extra protection of an eVent top on the bivy.

I also have a seam sealed/"waterproof" Marmot Helium EQ.

I've spent a night in a raging storm in my Contrail where one of the stakes pulled up out of the mud and I spent the night under my collapsed tent in a puddle of mud. Thank god I had seam sealed my sleeping bag. I spent a long night literally curled up in my bag with the head area completely cinched up tight to keep water from coming into my bag. I did manage stay dry and warm. I looked like Han Solo in carbonite the next morning with the tent collapsed on me the next morning.

The Contrail did fine, I just did not secure my stake in the ground well enough. I should have put something on top of the stake to further secure it. Not the tent's fault. User error!

After that experience, I am really cautious and paranoid about water and getting soaked.

My observation about the Contrail is that because of the need for ventilation to prevent condensation, it does not provide much warmth. I hope that the bivy will trap more body heat to allow me to use a lighter sleeping bag.

P.S. I wanted to say that the online subscription alone is worth every penny just for the great information that I have gotten from the forums. I am a newbie with only about 1 year experience going light weight. Thanks to everyone for the feed back for my newbie question.


barry hitchcock
(barryspoons) - F
bivi w/o dying on 12/09/2007 14:26:07 MST Print View

robert---when sealed up in v cold weather i burn a nightlight for light and heat?---if that rear ventilation hole is too small i guess me and the candle will both be extinguished

Edited by barryspoons on 12/09/2007 14:29:29 MST.

Richard Matthews
(food) - F

Locale: Colorado Rockies
Re: Why I love this website on 12/09/2007 18:33:52 MST Print View


I have an ID Unishelter and a MLD Alpine bivy. I leave the bivy unzipped about a foot and prop it open with a water bottle.

Yes, a bivy adds about 10 degrees over a hammock or tarptent style shelter.

Jake Calabrese
(trekmore) - F

Locale: Colorado
weight? on 12/09/2007 19:23:59 MST Print View

So what does all this weigh? I never solo like it appears many or most posters do, so I nearly always have a tent which divided by 2 makes the weight rather low (for the value)... So what does the tarp/bivy/stakes/guys/etc. weigh?

- Jake

Tony Wong
(Valshar) - MLife

Locale: San Francisco Bay Area
Bivy & Poncho Tarp Weight on 12/10/2007 00:30:02 MST Print View

Given that I using the "heaviest" MLD Bivy at 12 to 13 oz. and a 9 oz poncho tarp, the weight is pretty much the same as the solo Henry Shire Contrail Tarp Tent that I have been using.

The weight savings that I see is found in not having to carry a 12 oz rain jacket.

I am also hoping that by using a bivy over a tarp tent, I can reduce weight by using a my Marmot Atom 40 degree/1 lb sleeping bag vs. my 2 lb 3 oz Marmot Helium EQ 15 degree bag.

Optimistically, I am hoping to cut 1 lb 15 oz from my setup.

Basically, this is an expensive experiment to try to save almost 2 lbs of weight.

I don't travel solo and don't plan to in the future for safety reasons, but I do setup my gear on the assumption that I solo/totally self reliant.

P.S. Calling this is an expensive experiment is not a knock against MLD. The bivy an poncho tarp that I received is extremely well made. The sewing is tight and straight. It is obvious that a lot of care was put into making it. I can't wait to get myself into bad weather with it. :)