Big Agnes Three Wire Bivy Sack

Big Agnes shows an eVent hooped bivy.

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by Mike Martin | 2007-01-30 21:20:00-07

The Big Agnes Three Wire Bivy Sack is squarely aimed at the Integral Designs Unishelter. Both are made of three-layer eVent fabric, and both have claimed weights of 31 ounces. The Three Wire Bivy Sack uses a two-pole design very simlar to the 26 ounce (claimed) Black Diamond Lightsabre, but is made of fully-waterproof and highly breathable eVent fabric rather than the lighter, but water resistant EPIC fabric used by Black Diamond. The two-pole design provides more head room and potentially offers increased stability and wind resistance when compared to the single-hooped Unishelter, but the Unishelter offers more ventilation options with its tunnel vent.

The debate as to which is better - eVent or EPIC continues to rage. Three-layer eVent is fully-waterproof, but heavier than the lightest EPIC fabrics. In the fabrics used in currently available bivy sacks, EPIC is more air permeable, but has a lower moisture vapor transmission rate (MVTR) than eVent. EPIC’s breathability can suffer at temperatures just below freezing. Which is better depends on the intended use - for shower protection at above freezing temperatures, or deep winter use, an EPIC bivy will save you weight; an eVent one (properly designed and seam-sealed) will provide greater protection against sustained rain and condensation in sub-freezing conditions.

Three Wire Bivy Sack Features

  • Trail Weight of 31 oz
  • eVent top fabric - fully seam taped
  • Nylon ripstop bottom fabric (presumably with a waterproof coating)
  • Mesh bug netting closure
  • Peaked visor and zipper flap over head opening
  • Available June, 2007
  • MSRP $299


Citation

"Big Agnes Three Wire Bivy Sack," by Mike Martin. BackpackingLight.com (ISSN 1537-0364).
http://backpackinglight.com/cgi-bin/backpackinglight/02785.html, 2007-01-30 21:20:00-07.

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Big Agnes Three Wire Bivy Sack
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Forum Admin
(ForumMP) - BPL Staff - F
Big Agnes Three Wire Bivy Sack on 01/30/2007 21:20:02 MST Print View

Companion forum thread to:

Big Agnes Three Wire Bivy Sack

Brian James
(bjamesd) - F

Locale: South Coast of BC
Re: Big Agnes Three Wire Bivy Sack on 01/31/2007 08:35:46 MST Print View

I re-read that Bivy comparo 3 times and I still don't get what they mean by "tunnel vent."

Could someone enlighten the ignorant?

Michael Martin
(MikeMartin) - BPL Staff - MLife

Locale: North Idaho
Re: Big Agnes Three Wire Bivy Sack on 01/31/2007 08:43:43 MST Print View

>> I still don't get what they mean by "tunnel vent."

A tunnel vent is a tube of fabric, say 4 to 6 inches in diameter and 6 inches long, often with mesh covering one end and a drawcord closure. Integral Designs uses them extensively in their tent and bivy line.

Cheers,

-Mike

Edited by MikeMartin on 01/31/2007 08:49:44 MST.

Dave U
(FamilyGuy) - F

Locale: Rockies
Re: Re: Big Agnes Three Wire Bivy Sack on 01/31/2007 08:44:11 MST Print View

There is a tunnel vent on the eVENT Unishelter that is about 2/3rds up from the bottom of the head area of the bivy shelter. I extends out about 6 inches or so and can be closed off or opened - it has a mesh insert.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Big Agnes Three Wire Bivy Sack on 01/31/2007 10:00:05 MST Print View

Brian, here's a link to the ID bivy webpage

Take a look at the Crysallis and eVENT Uni (regular Uni lacks the tunnel vent). Also, the eVENT Crysallis doesn't have mesh covering the tunnel vent (eVENT Uni does) - guess ID doesn't feel it's needed with the internal full mesh enclosure that is found in the Crysallis.

Brian James
(bjamesd) - F

Locale: South Coast of BC
Re: Re: Re: Big Agnes Three Wire Bivy Sack on 01/31/2007 10:46:51 MST Print View

Aaah... it's that chimney thing. Thanks for the clarification!

I've studied the ID bivy pages (actually pretty much everything ID sells) quite a bit -- I guess I just had a conceptual disconnect regarding "tunnel".

On the subject, how does the Tunnel vent really work in the Crysallis? I understand it venting warm, moist air out the top, but how does cool exterior air get *into* the sack so that I can breathe? It seems to me that any opening in that zipper (in a storm) is going to be a water intake-port... unless I hold very still and rig the fabric just so. And if I don't open the zipper, I would destroy the convection current that's sucking all the moisture out the top.

Maybe I could take an oxygen bottle, or just hold my breath for a really long time?crysallis

PS you can see in the image that the zipper is distinctly skyward-facing. Now that the flap over the zipper has been eliminated, how am I supposed to crack this zipper during a straight-down heavy rainfall?

Edited by bjamesd on 01/31/2007 10:50:45 MST.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Re: Re: Big Agnes Three Wire Bivy Sack on 01/31/2007 10:54:19 MST Print View

On the prev. gen. non-eVENT Crysallis, a rain/storm flap covered the zipper. It would be left open a few inches. Just rcv'd the eVENT Crysallis two days ago & haven't used it yet. My guess is that you've got to leave the zipper open a tad & try to get the zipper facing downward. It could be a weak point in the design? On the up side it only weighs 24.9oz on my digital scale until it takes on water through the partially open zipper!

Actually, maybe my "hot air" just rises out of it when i exhale & then cooler, drier air enters through the same tunnel vent - sort of the equivalent of half-duplex communications in telecommunications.

I'd say from laying in it (that's all i've done thus far) that the zipper ISN'T skyward facing. It's sideward facing. Could I move in such a way that it could become skyward facing? Suppose so, especially since there weren't any stake-out loops i could find on mine.

Edited by pj on 01/31/2007 10:58:00 MST.

Brian James
(bjamesd) - F

Locale: South Coast of BC
Re: Re: Re: Re: Re: Big Agnes Three Wire Bivy Sack on 01/31/2007 11:19:26 MST Print View

Thanks for the info and sorry to hijack the thread.

I didn't know you were getting the exact bivy I was drooling over; sorry to state so many misgivings. I should have qualified my remarks with the fact that it seems like the almost-perfect all-season all-trip bivy, which is why I've scrutinized it so hard. I live in Vancouver (climate like Seattle) so every single gear decision takes steady, driving rain into consideration. When I plan a trip, I plan for 24-hour-a-day rain for the entire week...because it's entirely possible.

I'd really love to hear your experiences with your new bivy; congratulations! Specifically, whether you can find a way to rig the zipper so that it can be open a couple of inches during pouring rain. I suppose one could always put a jacket over it too or else camp at the base of a tree during rainstorms. Orrr... can the tunnel be held tight to the face like a snorkel for perfect ingress-egress venting wiht every breath?

Anyway thanks again for the info!

Brian

Dave U
(FamilyGuy) - F

Locale: Rockies
Mesh on 01/31/2007 12:14:14 MST Print View

PJ, is the mesh on the Chrysallis 'propped' up or does it just lie against your face when zipped up?

So overall impressions...is it a keeper?

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Brian & James, about our dear Crysallis... on 01/31/2007 13:06:17 MST Print View

In an attempt to keep from improperly inflating my Rank, i'll ans. both of you in ONE POST.

My short-term mem is very poor for the last six yrs.

Only remembered this a few minutes ago as i read your Post, Brian. Perhaps the following is so b/c i'm so very short, but the Crysallis (ID's spelling, which is diff fr/REI's Chrysalis tent) is long, so maybe the following would be so for taller users also?

The portion of the zipper nearest the top of my head might easily become slightly downward facing in use. I noticed it both sidewards facing and even slightly down, depending upon my movement & my attempts at positioning the bivy fr/within when i had it (shhh...don't tell anyone) ALL ZIPPED UP. Since it can't be staked down, i wouldn't trust it to stay that way throughout a night of use. Even when facing slightly downward, it didn't look like the zipper could get accidentally immersed in a puddle, unless intentionally forced.

And yes, Brian, you have a future in mind-reading. The tunnel-vent can be positioned very close to the face. But, again, i don't know whether it would stay there. Now there's yet another use for duct tape! Tape the vent to my nose!

James, the mesh fell all over my face, but i wasn't wearing my ballcap at the time which i sometimes wear sleeping just for that purpose (like in other bivy sacks, lacking a wire or hoop). But there was a small loop, centrally located on a horizontal seam on the mesh, to allow tying it off to a well positioned branch or trekking pole. I'm also going to jury-rig something for when there is both light rain & some bugs. My intention is to use that loop and perhaps a strip of duct tape, or perhaps some small very sticky back velcro dots (i'll sew one side to the tie-up loop on the mesh & stick the other side to the dome) to temporarily afix the mesh loop to the wire-stiffened eVENT dome. Don't want the bugs coming in through the un-meshed tunnel vent or the partially unzipped zipper. Zipping the mesh up will prevent this, and hopefully the jury-rig will keep the mesh up near the dome and off of the face. I don't think it will be hard to accomplish this even though my name isn't Bill Fornshell. I was hoping it would have some form to it and maybe i could figure out how to insert a fine wire (much finer than is in the eVENT dome) into the mesh seam (or better yet tape it to the inside of the seam?). I don't think it would take a very thick wire to have the necessary stiffness to hold the mesh somewhat off of the face. Wish it still had the rain/storm flap over the zipper - i'd feel more secure.

This is probably a keeper. I really like the simplicity, the light weight, the small packed volume, and, of course, the eVENT fabric. The issue will be water entry since i really wanted a very simple bivy for use in heavy rain, yet still have a lot of mesh for hot weather use. There are times, however, when i like to put a stake or two to hold the bivy down so that it doesn't blow away in very heavy winds - something which i won't be able to do. Also, I'd rather NOT have to use anything external to the bivy to hold the mesh off of my face when the eVENT dome is unzipped and rolled down near my chest or waist.

Any other questions?

Brian James
(bjamesd) - F

Locale: South Coast of BC
Re: Brian & James, about our dear Crysallis... on 02/01/2007 17:27:27 MST Print View

Great info; thanks!

I look forward to reading more about your experiences; particularly during "bivy-challenging" conditions and during heavy rain!

Brian

John Carter
(jcarter1)

Locale: Pacific Northwest
Big Agnes Three Wire Bivy Sack on 02/01/2007 18:36:07 MST Print View

Any word on availability?

Bill Fornshell
(bfornshell) - MLife

Locale: Southern Texas
Wire Hoop for a Bivy on 02/01/2007 19:19:03 MST Print View

pj said:
"I was hoping it would have some form to it and maybe i could figure out how to insert a fine wire (much finer than is in the eVENT dome) into the mesh seam (or better yet tape it to the inside of the seam?). I don't think it would take a very thick wire to have the necessary stiffness to hold the mesh somewhat off of the face."

pj,
Do you have any of that BMW - Ti wire. I used some really small surgical tubing about 3 inches long as a splice to connect two pieces of Ti wire together for a hoop. You might try that.

Frank Ramos
(frprovis) - F
Re: Bivies on 02/01/2007 20:57:25 MST Print View

I'm not sure what all the hoopla is over Epic and Event and bivies. In my experience, nothing will breath when it is covered with water, whereas Goretex works fine for bivy sacks in dry conditions. Yes, you may get condensation in the foot area of your sleeping bag or quilt with Goretex, but you will also get condensation in the foot area using just a tarp, under certain conditions, so I fail to see what the big deal is over Epic and Event. For a wind shirt, I understand the importance of high moisture vapor transmission, but for a bivy?

I spent an entire season hiking with a modified Outdoor Research bivy, with coated nylon bottom and Goretex top. They no longer make the model I used and in any case, my modifications changed the design significantly, but it was sort of like the current OR Advanced Bivy. That is, you could prop the clamshell hood open during driving rain and both keep the rain out and also allow some fresh air in so you didn't feel stifled. My conclusions from this experience:

1. If you encounter long periods of heavy cold rain, then expect to lose loft with a down bag. I repeat: no fabric can possibly breath when it is covered with moisture from heavy rain.

2. You should try to walk barefoot now and then to keep your feet scraped clean of fungus, because they won't have a chance to dry out in the bivy. The rest of your body will also feel grungy when it is raining, but unlike your feet, the rest of your body is able to air out during the day and hence is much less likely to develop funguses.

3. If you sleep on your back, then your breath will condense on the top of the bivy to the point where eventually there'll be a steady rain down on your face. Most uncomfortable and also a good way to lose loft in a down bag/quilt. The problem will be lessensed, though not eliminated entirely, if you sleep on your side with your mouth close to the air gap.

4. Make sure you empty your bladder before going to sleep, because getting in and out of a wet bivy at 3 in the morning, especially if it is still raining, is a royal PITA. All the moisture you pick up in the course of this nighttime call of Nature will evaporate inside the bivy, be unable to escape due to the coating of water on the outside of the bivy (assuming it is still raining), and thus eventually get into your sleeping bag/quilt.

5. The OR bivies came from the factory with a nasty fishy smell which got worse with time, since added to the fish smell was the smell of mildew. Most of the problems were with the OR coated nylon bottom and the uncoated nylon tie-out loops. (These loops took forever to dry. I cut most of them off, but the part in the seam that I couldn't cut off still absorbed moisture and then developed mildew.) The goretex top was never a problem--no mildew, no smell, no condensation except during heavy rain.

6. The bivy was extremely uncomfortable in warm conditions, whether rain or not raining. In particular, the sun in June didn't set until after 9pm and the bivy was very uncomfotable prior to then. But I wanted to make camp at 6pm and lie down for a few hours. I couldn't lie comfortably on top of the bivy because of hordes of flies and sometimes mosquitos. This excessive warmth was my biggest gripe about the bivy and is why I now use a hand-make bug-bivy under a tarp.(http://www.geocities.com/frhiking/sewing_bugbivy.htm).

Of the 100 or so nights I spent sleeping outdoors that season, only about 10 had significant rain, as I recall. When it didn't rain, I really liked sleeping in the bivy. But after the novelty of using the bivy during heavy rain wore off, I started to pay close attention to the weather, so as to make sure I was in a hotel when rain threatened. That suggests that the bivy was something of a failure at dealing with heavy rain. I abandoned the bivy after this trip and have no intentions of using a bivy again as my sole shelter.

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Wire Hoop for a Bivy on 02/02/2007 03:55:12 MST Print View

Bill, i do have the Ti wire. Thought about it. It might work. I really want to try something with maybe 1/4 to 1/2 the diameter of the Ti wire. Also, I've yet to try to "yield" (2b-understood in the proper "materials" sense) the BMW Ti wire and change its spring constant/rate.

Whatever wire i use must yield easily, yet retain enough strength and not suffer fatigue failure after a "bunch" (not2b understood in any technical sense) of damaging cycles. Everytime it's bent to a new shape that it essentially retains to some degree, fatigue damage results. So, it must have good fatigue characteristics, strength, and be of a fine diameter.

The BMW Ti will be my "safety valve" if i can't come up with a better wire. Actually, i'm bettin' that you'll beat me to it and come up with an ideal sol'n for me!!

paul johnson
(pj) - F

Locale: LazyBoy in my Den - miss the forest
Re: Re: Bivies on 02/02/2007 04:36:10 MST Print View

Frank, you might recall from old Posts of mine how much i respect your opinion, especially since you know a ton more about backpacking than i do. However, let me attempt to address your points with some possible solutions. Are the solutions perfect? By, all means, NO! Are they somewhat workable? Yes. Do they work better in some conditions than in others? Yes.


>>"1. If you encounter long periods of heavy cold rain, then expect to lose loft with a down bag. I repeat: no fabric can possibly breath when it is covered with moisture from heavy rain."

Loss of loft is expected. It happens even in non-bivy shelters to some degree, depending upon the conditions.

The key to keeping Epic, eVENT, and other WPB fabrics performing optimally (this doesn't imply that they are great by any means, just performing up to their inherent capabilities, whatever they may be), is to keep the DWR finish clean and performing properly. Granted in long term, heavy rain, this can be overwhelmed. However, in my personal experience which may not translate well for other since i sweat very little, it is my exhaled breath that contributes to most overnight moisture build up, but more on that later...


>>"2. You should try to walk barefoot now and then to keep your feet scraped clean of fungus, because they won't have a chance to dry out in the bivy. The rest of your body will also feel grungy when it is raining, but unlike your feet, the rest of your body is able to air out during the day and hence is much less likely to develop funguses."


I use either off-the-shelf powders or anti-fungal ointments, or jewelweed (aka touch-me-not) preparations, either made at home, or picked, if encountered, while on a trek. Sweet fern might also be used for this purpose as well, but doesn't work, IME, quite as well. BTW, both are excellent poison ivy remedies. Jewelweed contains natural anti-fungal properties, first recognized, by pharmaceutical companies in the late 60's, IIRC, but used for centuries by Native Americans in New England.


>>3. If you sleep on your back, then your breath will condense on the top of the bivy to the point where eventually there'll be a steady rain down on your face. Most uncomfortable and also a good way to lose loft in a down bag/quilt. The problem will be lessensed, though not eliminated entirely, if you sleep on your side with your mouth close to the air gap."

Now, for more on that breath...

Some bivies i have address your legitimate concern/observation. I'm a back sleeper (your comment on side-sleeping is appropriate for the OR clamshell/croc-mouth opening bivies). When i use a wired bivy (NOT clamshell/croc-mouth opening), i place the opening very close to my nose. The majority of my breath escapes and doesn't result in contributing, relatively speaking, much moisture to the bivy environment. While i like the more roomy bivy shelters, which use a sectioned, shock-corded hoop pole (e.g. ID eVENT Unishelter, & BD Lightsabre), they are harder to accomplish the same effect since the opening is further away from one's nose. Some bivies, like the defunct TNF Soloist, and the current, relatively inexpensive, Chinook Summit bivy (which i've only used once thus far & no rainfall occurred) use a really nice cross-ventilation design in the hood area. If there is any breeze this works better at evacuating moisture than in the ID Uni's. The eVENT Uni has a tunnel vent which helps do the same thing, but not quite as well as in the Chinook Summit bivy.


>>4. Make sure you empty your bladder before going to sleep, because getting in and out of a wet bivy at 3 in the morning, especially if it is still raining, is a royal PITA. All the moisture you pick up in the course of this nighttime call of Nature will evaporate inside the bivy, be unable to escape due to the coating of water on the outside of the bivy (assuming it is still raining), and thus eventually get into your sleeping bag/quilt."


So, right you are. Two solutions:
1) wide-mouth pee bottle with standard disclaimer: "Kids, don't try this at home. Well trained, professional UL hiker in a 'closed' bivy." Actually, in this case, home practice might be in order. Remember, "practice makes p--fect!"

2) [a]i don't drink 45min b/f turning in; [b] i, hopefully, stay warm nicely ensconsed in bag&bivy, and my bladder doesn't fill due to constriction of peripheral blood vessals in an attempt to maintain core temp.; [c] when i wake up is when i break camp & begin hiking (that is, when i'm solo - perhaps this, in part, explains why i have so few trekkin' mates) - i'll eat b-fast either on the move (if NOT cookin' & not just consuming a super-GORP only fare that trek), or later, at or after dawn breaks if i'm heatin' water for oatmeal & b-fast tea.


>>"5. The OR bivies came from the factory with a nasty fishy smell which got worse with time, since added to the fish smell was the smell of mildew. Most of the problems were with the OR coated nylon bottom and the uncoated nylon tie-out loops. (These loops took forever to dry. I cut most of them off, but the part in the seam that I couldn't cut off still absorbed moisture and then developed mildew.) The goretex top was never a problem--no mildew, no smell, no condensation except during heavy rain."

I can't stand those pad retention loops either in my OR bivies. My bivies are now all newer & i don't notice much of an odor, other than some sort of "new bivy" chemical smell which lessens with use & airing out.


>>"6. The bivy was extremely uncomfortable in warm conditions, whether rain or not raining. In particular, the sun in June didn't set until after 9pm and the bivy was very uncomfotable prior to then. But I wanted to make camp at 6pm and lie down for a few hours. I couldn't lie comfortably on top of the bivy because of hordes of flies and sometimes mosquitos. This excessive warmth was my biggest gripe about the bivy and is why I now use a hand-make bug-bivy under a tarp.(http://www.geocities.com/frhiking/sewing_bugbivy.htm)."

Bivies just aren't as comfortable as tents or especially tarptents in the very rainy, humid, or hot weather. Have to agree with you. They just ain't, and that's a fact any bivy user will have to live with. This is true even in good weather, and even more noticeable in bad weather. In my case, i make camp later (i don't need much sleep, but sleep REAL soundly when i do sleep & fall asleep in typically 30sec to 2min - again, a personal thing which makes bivy use more "livable" for me) and usually am under tree cover, so sun heatin' up the bivy isn't too much of an issue. I eat dinner generally 1/2mi or 2 or more miles away from my planned bivouac time/site - a, perhaps naive, attempt to minimize food odors near my chosen bivouac site.

Bivies can be stifling in hot & humid conditions. When the weather is good, a bivy with bug netting down to the waist is the way to go. In similar hot & humid conditions coupled with rain, i am either under conifers with some low branches to minimize rainfall (or a rock ledge - which is harder to find), or i pitch a cape or poncho-tarp over the bivy, or i zip-up, shut-up, and put-up! No sniveling that my momma' ain't there to 'shoo' the skeeters away.

In my case, i'm enjoying floored tarptents more and more. If i knew that i'd be able to pitch one anywhere i might be trekkin', i'd probably use one more. However, in many places, real-estate is at a premium when stealth camping up in my neck-of-the-woods & a bivy makes it so much easier to find a nice out-of-the-way stealth site. I always have the option of pitchin' a PT lean-to style over the bivy if need be.

Are my solutions/responses "perfect". NOT AT ALL. However, they are workable or at worst tolerable for me. YMMV. HYOH.

Eric Blumensaadt
(Danepacker) - MLife

Locale: Mojave Desert
AT LAST! on 02/03/2007 21:43:27 MST Print View

At last, a bivy that REALLY breathes!...and is very waterprof.

Eric

Edited by Danepacker on 02/03/2007 21:46:34 MST.