Most Breathable Bivy?

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).

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"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.

"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.

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 ;)

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Still not ready to MYOG. Sorry, but it's not the route I want to take. I appreciate the advice.

Not looking at the Frog Togs either. I'm also pretty sure what kind of setup I'm looking for, and it's Bivy + Tarp.

About bugs, some of the worst nights I've had with skeeters have been during rainstorms. They flock to a tarp and hang out. I'm not risking a headnet, I'm going for full mosquito coverage.

Thanks for the continuing information. I'm in the process of working through the posts.

If you're getting a full size TS, I agree with others that there's basically zero reason for a WPB bivy. Any non-WPB fabric will be far more breathable than the most breathable WPB, even Event. M90 from Borah gear is 80 bucks and you could get it made however you want.

" Any non-WPB fabric will be far more breathable than the most breathable WPB, even Event. "

While that's a true statement, that doesn't mean a more breathable fabric is better for use in a bivy when condensation is of concern.

This is a very good article,and so is this one.

~"Vapor permeable fabrics have membranes that absorbs water like paper. The water once in the membrane works its way to the outside where it again turns to vapore and is carried off. Air however will not flow through it. Most WPB fabrics that use polyurethane membrane are only Vapor breathable and they typically don't breath much until interior humidity gets high. Breathability specs for polyurethane WPB fabrics are typically well below Event. Also you won't see a CFM rating for polyurethane WPB fabrics simply because air won't flow through the membrane. Pertex Shield is an example of this type of fabric. I don't think vapor permeable Membrane fabrics are a good choice for bivy's

Air permeable fabrics like event have very small holes that allow air and vapor through but don't allow or make it very hard for liquid water to get through. Event has a hydrostatic head of about 25,000mm and a CFM rating of 0.5 (If I remember correctly). If you increase the breathability (higher CFM)the hydrostatic head goes down. So when you get to ordinary fabric such as Momentum 50 your hydrostatic head goes to almost zero and the CFM ratting goes very high."

Read this, it's on Page 3.

" Any non-WPB fabric will be far more breathable than the most breathable WPB, even Event. "

Yes but not in the conditions that you think with respect to eVent (as described earlier). As your body temperature goes up, the temp differential as presented as moisture is pushed through the bivy and condenses on top of the fabric. With eVent, that is a minor inconvenience. You wipe it off or it rolls off but you remain dry. With a non-WPB fabric, the fabric then wets out and gets you soaked.

I have used many bivvies over the years, including several eVent bivvies including the Integral Designs eVent overbag. With that bivy, I have never once, and I mean never, had internal condensation in temperatures ranging from 50F to -10F, in the snow, desert, and by water sources. I have been soaked in a bivy made of momentum fabric (MLD) and had condensation on the floor (70d pu coated) of an eVent bivy but never in that overbag.

Highly recommend reading some of the BPL articles on the subject and as well, reviews of specific eVent bivvies and clothing available on this site.

Going outside the box a little how about the TT Notch inner nettent that has partially solid sides?:

The advantages with eVent bivys that I've read of seems to typically be below freezing (haven't used a WPB bivy myself, though I've made a few out of various DWR fabrics). If a primary you're wanting it is for mosquitos, I'm assuming it isn't for that cold of conditions. Some kind of nest or innernet seems a lot more appropriate than a bivy for what you say you want to use it for. A trailstar provides some serious coverage. Even though it doesn't pitch completely to the ground, you aren't going to get wet from blowing rain. Snow, maybe, in which case it might be cold enough that a synthetic overquilt would be more appropriate than a bivy anyway for moisture management and bugs probably aren't an issue.

People seem to be misinterpreting my purpose. You recommend something for one condition and then ignore a second condition. I need this bivy to do MULTIPLE things well, not just one scenario. It's not relevant if there are no bugs in the winter, my bivy needs to be bugproof.

A) As with anything, I'm not made of money. if I buy one system that works in three potential conditions, I'm way ahead than buying for just one condition.

B) I know that spindrift and wind are an issue under a tarp. Some people keep repeating "Just tie down your tarp tight!" but it's not quite that simple. A lot of terrain won't allow a "waterproof" tarp pitch. The bivy bag is my second layer of protection.

C) Redundancy in a shelter is useful if you're taking it for storms. If I can't get my tarp to pitch or if the conditions are too rough for it, and I have a bivy, I may just save my life.

So, Thank you for the tent suggestions and the advice, but I am still JUST looking for what's in the OP.

Thanks,
M

In fairness, nobody can read your mind. You seem to add requirements all the time that aren't in your original post. Moreover, if "price is no consideration" as said in OP, then having multiple setups should be an option. Just sayin.

Also, if you're now thinking of taking this setup into winter storms you might want to check on that. Trailstar is great in wind but I'm not so sure about snow. . .

So will you be selling your hammock system since it doesn't cover all scenarios you might encounter?

Yeah, I mean, I didn't say anything about snow. I just feel like if you make a Bivy thread and someone reccomends a Notch, it's off-track. My OP is pretty clear. I'm getting two conflicting points of view; some people say eVent has the least condensation, and some people say Water Resistant materials are the most breathable. Nobody can back that up with anything other than opinion, which I already have in spades.

Maybe it's an unanswerable question. I feel like if I ask which down jacket is the warmest, someone has a chart with actual quantitative data, but ask about a bivy… and you get a whole spectrum of ideas, advice, chastising, etc.

I don't think I've added a single thing to the OP… Storms, blocking wind/rain under the tarp, breathable, bugproof. Not everyone is off-track but some people are.

Money is no object since the ceiling for a bivy is like $400. I'm happy to pay for a good bivy. What I can't do is spend $2000 on a multiple shelter system. Plus, on longer trips I need one setup to cover the spectrum.

I mean it when I say I appreciate the off-track stuff, I just need the on-track stuff more.

And no, I'm not selling my hammock. OP says, can't always use a hammock!

Max,
I can back up my very rare condensation claims with over 100 bivys in use.
Buy and Uber Bivy and take it out for a night in a nasty storm.
You will sleep warm and dry. If not, send it back, and I'll refund your money.
Sounds like a common sense approach to solve the question :)

Max,

I'd definitely take David up on that offer. How can you beat that?

No bivy will do what you are wanting very well in this range of situations.

This might suck the least at accomplishing the things you want:

http://www.exped.com/exped/web/exped_homepage_int.nsf/0/77CDB11B04309DC6C1256F2B002E724D?opendocument

I couldn't find one for sale. mountainequipment.com has one with PU floor. Maybe MLD will make one to your specs. Either will likely be more expensive than 2 separate specialized products.

Actually, that offer extends to everyone. As long as you use the groundsheet and don't drag it through the woods, there will be no wear on the bivy. I've got over 25 nights in mine, with no detectable wear. I'm that confident that this bivy is a game changer. I love sleeping in storms :)

David,

The uber looks great and I'm tempted by the double as it seems my daughter might join me on the wonderland this summer. Is it possible to add a tie point to use in lieu of a hoop and if so, how much weight would I save by forgoing the loop?

Edit: What are the packed dimensions of the Double uber? I may have overlooked it but I didn't see that on your website.
Edit edit: If it was a snake it would have bit me. 6" x 18"

The conflict isn't the POVs…its your interpretaion. Breathability isn't the only determining factor for wetness inside bivy. If you use a goretex bivy in a thunderstorm (no tarp) it will fair much better than one made of m50.
I've had copious condensation on a net tent inner

Event is less breathable than typical wrb by an order of maginitude in most cases.

David Ure has posted multiple times that he doesn't get wet in Event..many others have posted the same elsewhere. You don't have to look hard for people saying wrb condesation happened.

There aren't CFM numbers for everything, but for quite a few.

http://www.backpackinglight.com/cgi-bin/backpackinglight/forums/thread_display.html?forum_thread_id=45026&disable_pagination=1

edit: Why don't you just buy the trailstar, take it out in a gnarly storm in the yard or on an overnight, and figure out what your needs actually are rather than theorizing on the interwebs without having used any part of the perfect system you're trying to put together.