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Most Breathable Bivy?
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John Harper
(johnnyh88) - MLife

Locale: The SouthWest
Re: Tyvek Bivy on 03/05/2013 07:57:31 MST Print View

I have a double bivy from Miles Gear - and while I've only used it a few nights, I've never had any condensation problems. On the other hand, I almost always had condensation with my Big Agnes Fly Creek UL2.

The upper material he uses is very breathable and waterproof; he describes it on the "Uber Bivy" page. The only downside is that it is a little bulky IMO, but this may be because he uses a Tyvek floor. The bivys come seam-sealed if you want and you have several options. He built in a mesh screen at the entrance for me.

Anthony Weston
(anthonyweston) - MLife

Locale: Southern CA
bivy on 03/05/2013 08:13:08 MST Print View

" I am buying this for cold, wet, windy storms in the middle of clearings."

For these conditions I use a Duomid with a montbell breeze tec bivy (8oz) and completely waterproof.

Bivies by themselves will not keep you dry.

The Duomid is great in the wind and rain. The Montbell bivy handles any spray that comes in or flows under if the clearing becomes a lake.

The Montbell Breeze Tec breathes well and is lighter than event and costs less.
It doesn't have a full hood but you don't need it with the Duomid.

In the winter, for wind and snow I used the Integral designs Wedge Bivy which I picked up on ebay for 1/2 price.

Also Locus Gear in Japan has a new Pneuma Bivy eVent which is 10oz but $331 for the large.

Anthony Weston
(anthonyweston) - MLife

Locale: Southern CA
Montbell on 03/05/2013 08:22:17 MST Print View

I actually put the Montbell breeze tec bivy in the bathtub with 2 inches of water for several hours and the paper towels I had inside came out dry. The seams are taped.

Dave -
(FamilyGuy) - F

Locale: Up there
Re: Montbell on 03/05/2013 08:27:33 MST Print View

Are you looking for the most breathable and still waterproof or are you looking for the most breathable? Most breathable is no bivy at all (Ha). Most breathable and waterproof is eVent, and I would also argue more breathable than any fabric below freezing. At least this has been my experience.

Max Dilthey
(mdilthey) - M

Re: Re: I don't MYOG on 03/05/2013 08:28:47 MST Print View

--"I have scoured the internet and there is no miracle fabric, all bivies have condensation/frost from time to time but the ones with the least mentions of condensation are made of all eVENT like the Integral Designs All eVENT bag cover (now discontinued) and the OR Advanced Bivy, both with vapor and air permeable top fabrics. [8, 9, 10]

You say the OR Bivy is eVent but their site says GoreTex Respiration 3-layer fabric. Something I don't know?

I actually like the OR Bivy.

Anthony Weston
(anthonyweston) - MLife

Locale: Southern CA
bivy on 03/05/2013 08:50:15 MST Print View

These days I don't take any bivy, I use my duomid, an epiphany quilt which can handle the spray on it's own and a large gossamer gear 2 oz plastic sheet and a lighter tyvek for making kites. Most trips the plastic stays in my pack but if it looks like it will rain heavy I use the plastic and raise up the perimeter.

Ito Jakuchu
(jakuchu) - MLife

Locale: Japan
tyvek and event bivies on 03/05/2013 09:21:56 MST Print View

I just bought a cuben pyramid shelter from Locus Gear in Japan.
Looking at their other products I saw they have an all eVent bivy and also a tyvek bivy.



No relation or affiliation, just happy with a really well made product and buying experience, pretty short waiting time and general advice I got.

The site is in Japanese but if you send the owner an e-mail he will answer any of your questions in English. You can probably also order that way.

I personally got a Bristlecone bivy from Katabatic gear (silnylon bathtub/pertex upper with mesh) and it is made incredibly well too.

Can highly recommend any of these three options.

Edited by jakuchu on 03/05/2013 16:05:26 MST.

Daniel Fish

Locale: PDX
... on 03/05/2013 10:21:23 MST Print View


Edited by on 06/12/2013 00:27:43 MDT.

Alex H
(abhitt) - MLife

Locale: southern appalachians or desert SW
PU-PTFE's vs. PTFE only membranes on 03/05/2013 10:29:51 MST Print View

So this article answers most of these questions about standard Gore-Tex (a PU-PTFE) and eVent and eVent like PTFE only membranes (Exchangelite, Gore-Tex Respiration Positive, (used in some of the OR bivys), Gore-Tex FLO2 and Gore-Tex Windstopper

And some more details in this article

Dave -
(FamilyGuy) - F

Locale: Up there
Re: Condensation due to temp differential on 03/05/2013 10:32:36 MST Print View

The best way to handle condensation with a bivy is to not use one. The history of bivvy use is for high altitude mountaineering which involves below freezing temps. Condensation freezes and the ice can be shaken off.

With sub 1 pound shelters and highly water resistant sleeping bag shells, as well as highly water resistant down, bivy use really has become obsolete for backpacking. There are no benefits apart from draft protection for use with a quilt. But even then, with the additional weight of a bivy, just use a sleeping bag instead.

Daniel Fish

Locale: PDX
... on 03/05/2013 10:36:30 MST Print View


Edited by on 06/12/2013 00:28:21 MDT.

Alex H
(abhitt) - MLife

Locale: southern appalachians or desert SW
Re: Gore eptfe? on 03/05/2013 10:49:00 MST Print View

What Dave U said and read the articles I reference above about the PTFE's and the PU-PTFE's

Ian B.

Locale: PNW
Re: Condensation due to temp differential on 03/05/2013 11:31:01 MST Print View

"This would explain why the USGI bivy seems to have the best anecdotal reputation for low-condensation."

This was my experience over the years with the waterproof USGI bivy as well. Once I learned not to breathe into my bivy, my condensation issues were almost none. Too bad it’s 2.5 lbs. I've always used synthetic bags with my USGI bivy so maybe a down bag would have a different experience.

James Klein

Locale: Southeast
Re: Most Breathable Bivy? on 03/05/2013 12:30:03 MST Print View

I am trying to nail down exactly what you are looking for here...I think you are too.

You mention:
1)you are going to use the T.S. tarp when the weather is too nasty for the hammock or no trees.
2)you want something to protect your insulation from spray and wind chill
3)minimal condensation
a) not sure weather you need wbp or wrb
4)full coverage with a net window
a)no (minimal?) other netting
b)100% bug protection

I think bc of 1) you shouldn't need 4b (bc bugs typically arent around around in this weather) but I understand trips can span different bug/weather scenarios - maybe compromise with an open face bivy and a mosquito headnet?

I think if 2) is the main purpose: wrb material is the way to go. Id want a long zipper and the ability to suspend above your insulation. If it has integrated head netting I want to be able to unzip from above my head. I don't think anyone makes this so i'd see if borahgear or similar would make one to my specs.
But if you are willing to get past the bivy term i'd look at this inner made for the T.S's "normal" pitch: -- maybe you could get them to extend the nylon walls up much highter

If you are thinkingthe weather might ever be too much for the T.S. maybe consider the milesbivy or the locusgear event one(if it fits you).

Edited by jnklein21 on 03/05/2013 12:31:15 MST.

Justin McCabe

Locale: Southern California
RE: MYOG Tyvek on 03/05/2013 13:49:44 MST Print View

I also have no sewing skills to speak of. My first Tyvek bivy was made with no hood, no sewing, and held together by 3m super 77 and sealed with Tyvek tape. The only part I had help with is having someone sew the zipper on. Super easy, and the best part was I got to make it as wide/narrow as I wanted.

Then I got lucky and had my Mom sew me a Tyvek bivy with a trapezoidal foot box and hood (hurray for moms).

But, if you are thinking of an eVent bivy....the Pneuma eVent bivy by Jotaro at Locus Gear is dead sexy.

just Justin Whitson
Re: RE: MYOG Tyvek on 03/05/2013 15:47:12 MST Print View

Max, if you want a really simple, easy, and very cheap solution read on: Buy one of the heavier duty Frogg Toggs ponchos that has the snaps on the sides. Get some 2 or 3mil plastic--cut to size.

Plastic goes on bottom, completely unsnapped Frogg Toggs goes on top, and stuff some under your feet to keep it there.

If you really want extra protection, create a "bathtub" out of the plastic by folding in the corners, then taping them. This will raise the sides. Easy to do.

To secure the Frogg Toggs poncho onto the top of your body, you can do several things, such as loosely tie some cord around the top of it, tuck some of the very top into your bag or shirt near the collar area, etc

The Frogg Toggs can do double duty as your day raingear too. Its QUITE breathable, definitely more so than even eVent. Also, it's fairly light weight. While i don't like supporting Walmart personally (& try to as little as possible), you can find the heavier duty Frogg Toggs ponchos there for like 10 dollars.

I previously made a bivy via sewing, and using some expensive WPB fabric, zipper, etc, and i really wish i knew then, what i know now, because if i start using tarps i will just do the above since i currently have 2 Frogg Toggs ponchos (one really light weight emergency one, and the heavier duty one with snaps).

Daniel Fish

Locale: PDX
... on 03/05/2013 15:47:47 MST Print View


Edited by on 06/12/2013 00:29:04 MDT.

steven franchuk
Re: Condensation due to temp differential on 03/05/2013 21:38:00 MST Print View

"I've been thinking about the condensation issue. I'm wondering if there are 2 factors involved. 1 would be the ability to transfer warm wet air outside the bivy ( aka breathability ). But the other factor might be temp differential between the outside and the inside of the bivy.

Since the air inside the bivy will always have some moisture suspended in it, I would expect there will always be some condensation collecting on the inside of the bivy. I would also expect that this mechanism is more pronounced as the temp differential increases."

Temperature differential is part of it. You also need to consider body heat and dew point. The dew point is based on temperature and humidity. If the temperature is above the dew point no condensation will occur. If however the temperature drops below the dew point condensation will occur. Consider the following situations.

1 Very breathable bivy made of DWR fabric like Momentum. The high breathability of the fabric insures the humidity inside the bivy is likely going to stay just a little bit higher than outside. the high breathability also insures that any body heated air quickly gets out. This is a low temperature differential situation. If the air temperature drops to below the dewpoint water will start to condense outside and inside the bivy. You will get wet.

2. You keep the inside of the bivy heated so that it is always warmer inside the bivy than outside (A high temperature differential situation).the outside air temperature could drop below the dewpoint But do to the heat inside the bivy, the bivy stays dry because the inside stays above the dewpoint. You stay dry.

3. You are in a bivy made of waterproof fabric. Fabric that is not breathable. The temperature inside the bivy will be a little warmer than the the outide but humidity inside will increas because of the moisture released by your skin. A medium temperature differential situation. The depoint inside will increase thile the dewpoint outside stays stable You will get condensation inside because of the high dewpoint caused by the high humidity is above the temperature inside the bivy. Outside stays dry inside is very wet. This is a low temperature differential but high humidity ditterential situation. You will get wet in this situation.

4 you use a bivy made from WPB fabric that is Less breathable than DWR fabrics. Any additional humidity generated by your body creates goes outside. So inside humidity stays about the same as outside. The reduced breathability of the fabric blocks the wind insuring the inside temperature stays a little higher than outside. Outside the temperature drops below the dewpoint. Everything outside gets wet while inside the bivy stays dry. You stay dry.

As you can see it isn't just the temperature differential. You also have to manage moisture. A lot of people have been using DWR high breathable fabric to manage moisture. It doesn't take much effort to to find reports of condensation in DWR fabric bivys (situation 1). The Outside may be dripping wet due to condensation but the inside of your home is dry because it is heated (situation 2). Reading comments from those using event bivys I never see any comments about serious condensation. Is that because few people use Event bivys, or because Event makes it easy to get into situation 4? At night situation 4 is where you want to be. You will be warmer, dryer, and sleep more comfortably. Extreme weather changes may make it hard to stay in situation 4 in an Event bivy but fortunately Extreme events (very rapid outside temperature and humidity changes) don't occure frequently. And once the extreme weather is gone the Event bivy will start to dry out.

Edited by Surf on 03/05/2013 21:45:54 MST.

steven franchuk
Re: RE: MYOG Tyvek on 03/05/2013 22:01:47 MST Print View

"I can barely sew, and I have no machine, so Tyvek is out."

"also have no sewing skills to speak of. My first Tyvek bivy was made with no hood, no sewing, and held together by 3m super 77 and sealed with Tyvek tape. The only part I had help with is having someone sew the zipper on. Super easy, and the best part was I got to make it as wide/narrow as I wanted."

There is probably a glue out there that will have a very high bond to the zipper and Tyvek. However if there is not you can rivet the zipper to the fabric or use staples. There are snapps out there that are not held in place by a rivet or a staple like mechanism.

David Miles
(davidmiles) - F

Locale: Eastern Sierra
Re: Most Breathable Bivy? on 03/06/2013 01:59:05 MST Print View

Thanks John for the plug. I have a lot of bivy sacks out there and it's extremely rare to hear anyone talk about condensation. I would love to have a chance to compare it to an eVent bivy, but who has that kind of money. I know it blows away my GoreTex especially in freezing temps. If someone has an eVent bivy I would like to arrange a test. Please contact me.

By the way, I support MYOG since that's how I started many years ago. I can sell the top fabric for your projects. You just have to like white ;)

Edited by davidmiles on 03/06/2013 16:09:33 MST.