Bivy Question

more likely condensation. Can happen with the best of bivys.

Would a goretex bivy offer more relief from condensation? I typically go out when the weather is warm, so I opted for the Ti Goat bivy as well. My assumption is that the goretex would offer more protection from soaking rain, but actually have more condensation from the standpoint of the vapor having to pass through the membrane and some kind of outer fabric. I certainly hope the Ti Goat bivy is fairly breathable as it claims.

There was no condensation anywhere else in the bivy. Just at the spot where my feet went onto the wet grass, leading me to belive that it wasn’t that.

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Anyone else notice how doing a “refresh” on a page to see new responses posts your reply again? Software…

Epic or a DWR nylon would both “breathe” better than Gore-tex. Design of the bivy can be a factor–if the waterproof bottom of the bag is cut so that it comes up the sides of the Bag, you will have a greater chance of more condensation . This is a design defect of some cheap bivys I have seen in the past.

I like my MLD Soul Bivy–it has an Epic top ( modified to have more in the hood area) and a drawstring bottom end, so I can vent potential moisture better. No problems with the bottom leaking and it has shed light rain w/o recourse to a tarp.

Wade, are there any seams in the problem area of your bivy that could have leaked? Some very light sil nylons don’t take much to let water through. I don’t know what Ti Goat uses.

Condensation is the foot area of sleeping bags and quilts is very common. The feet generate a considerable amount of moisure from all the sweat glands, which continue working long after you finish hiking. The feet also pick up moisture if you walk around barefoot in moist grass before going into bed, or during an early AM pee-break. All this moisture then burns off in the night due to body heat. But the heat generated by the feet is seldom enough to drive the moisture all the way through the sleeping bag and/or bivy, so it condenses inside rather than outside the system. That is, the dew point in the foot area is inside rather than outside the bag. By contrast, the torso and head regions generate enough heat that the dew point (at least in 3-season camping) is usually pushed outside the bag and bivy. Things are different in winter. The dew point then is almost always inside the bag, unless your bag is very thin.

Does your bag perhaps have a very well insulated foot box, but no hood. This is a dumb idea of some bag/quilt manufacturers who never bothered to study human physiology and who never heard the old saying, “if your feet are warm, put on a hat”. The head gets first dibs on warm blood supply, then the torso, then the arms and legs, and the extremities get the residual. This is not a problem for the hands, at least while sleeping, since they can be kept close the head and torso. But it will be a problem for the feet if the head is not well insulated.

A properly insulated bag will have lots of insulation in the hood and torso but be skimpy on insulation in the foot box. This has two effects. (1) The feet feel warm because the body now has enough extra warmth to spare some blood supply for the extremities. (2) the dew point in the foot area is pushed outside of the bag, thus reducing condensation inside the bag. (Again though, things might not work so neatly in winter.)

The silnylon does not come up that high on the sides. Mabye a half inch bathtub bottom, but that is it.

Obvioiusly there is a seam along the entire area where the DWR nylon is sewed to the silnylon. The maker claims it uses hydrophobic tape along these seams.

It *could* have leaked thru the seams. It coudl have come thru the top thru the DWR nylon by brushing against my tarp’s bottom. It could have come thru the sil nylon bottom.

Any way you cut it, it failed under pretty negligable weather and leaves it suspect to ever withstand anything beyond this. I would never use this as my only shelter, nor could I see using it without a ground sheet at this point.

Note that the TiGoat literature indicates that you can use it to keep your bag dry from wet ground:

“The Sil bottom keeps your bag dry and protected from wet ground,
while the DWR top keeps wind blown rain and condensation off you.”

So, I guess its time to buy a new bivy. Wish the Bozeman ones were not so bloody expensive <grin>.

Has anyone tried the Equinox bivy?

Hi Wade,
If you are looking for a new bivy, you might want to check out Mountain Laurel Designs, a small outfit up in Maine run by Ron Bell. He makes very high quality bivys at a very reasonable price, and they are light as well. Also he is open to working with you on custom mods. I have been real happy with both his bivys and his tarps, and I’ll bet a lot of others who visit this website would agree from what I’ve seen. The website is http://www.mountainlaureldesigns.com Good luck,
Tom

I actually have a Devotion Bag on order from him right now. The wait is a bit long because of all the tarp/poncho orders due to the recent BPL test.

Regardless, a good idea to check out what he has in the bivy department.

I emailed TiGoat with the same questions as above and they have already responded. They are going to ship me a new bivy and request the old one back – he thinks it shouldn’t leak like that and wants to see why it failed.

Man, I love cottage industries.

Wade,
Frank Ramos nailed it, I think. You will almost always have more condensation in the foot area of a bag, and a bivy sack exacerbates the problem. Some bivies have ventillation capacity at the foot. That works as long as it does not admit rain. Look for a bivy with a spindrift collar and drawstring at the foot. That seems to work well. If you can ventillate the foot of your sleeping bag/quilt, that will help as well.

Wade, I have an Equinox bivy and experienced the same issue you had. I spent a week in the Indian Peaks of Colorado. We had an unusual amount of rain that week with night time temperatures in the low 40s F. I slept in a hammock, so moisture from the ground could not have been the problem. Everything was dry except the foot end of my bag. The bivy was brand new. I was using it as my pack as well, so the foot of the bivy was the bottom of my pack, and could have been damaged as a result. I did inspect it and found no observable damage. Condensation was my best guess but it seemed so localized. There was some wind, so it is possible that rain was the culprit though I don’t think so. Franks theory is the best I have heard. My bag was a WM Versalite which was definitely overrated for the temperatures experienced. I used it as a quilt.

Hi All,

I am new to the lightweight water-resistant/breathable bivy scene. I just acquired an equinox mummy bivy(my first bivy sack) and just experienced the footbox condensation issue mentioned above in this thread. This was condensation pure and simple and wetted out the outer fabric on the footbox of my sleeping bag.

My question is this: is this a common issue with bivy sacks in general or only with some bivy sacks? What are your experiences and recommendations?

Yes, it’s common.
One mitigation is by having a vent opening for the foot of the bivy. At least one bivy by Mountain Laurel Design, the “Soul Bivy”, has a drawstring operated foot vent. It does seem to help quite a bit.

In real cold temperatures, you can use a vapor barrier liner inside your sleeping bag which will remove body moisture as a condensation factor.

Frank Ramos, in a post above talks more in depth about condensation factors.

Would Vapor Barrier socks stop this condensation in the footbox?

Wade,
Yes, absolutely. And VBL clothing eliminates moisture loading the rest of the bag except for exhaled moisture. Some swear by VBL clothing for that reason and to sleep warmer due to the elimination of convective heat loss; some say they’re only bearable in sub-freezing weather; and some swear at them. See <warmlite.com> for a defense.

“Does your bag perhaps have a very well insulated foot box, but no hood. This is a dumb idea of some bag/quilt manufacturers”
Frank, The reason manufacturers of ultra-efficient/ultra-light sleeping bags like Nunatak make bags without hoods is because a bag hood cannot be practically worn while you are out of the bag. The first place I put my down is on my head neck and face. When it gets cold I throw on my 6oz. Himalayan jacket hood; whether I’m cooking breakfast, hosting a luncheon on a 13,000′ pass or stuck on an interminable belay. Do a few jumping jacks with that behemoth wrapped around your noggin’ and you’ll be instantly transported to the tropics. Add a 14oz. hoodless down quilt and I can sleep in freezing weather.
Al

Maybe this should be a new thread, but as somebody who’s never used a bivy, I’m wondering how the UL bivies, with an impermeable floor and a DWR nylon top, actually work.

Isn’t the top essentially the same material that’s already on the outside of a (non-uberlight) sleeping bag?

Do you get added protection just from having another layer, or a layer without seams, or is there some other process at work that I’m not getting?

Nathan,

I have the same question you have. I’ve read that a bivy bag will add some warmth to your sleeping bag (somewhere in the range of 10 degrees) and I have some friends who use them in tents for that purpose. However, the question still remains? For the cost of a typical 3 season bag and a UL Bivy sack you could get a fully waterproof 3 season bag that should be close to the same combined weight of a sleeping bag and bivy sack.

Just to add to the confusion, check out this article from Planet Fear:

http://www.planetfear.com/article_detail.asp?a_id=425

I’ll share my limited experience here and “parrot” things that I’ve read here over the last couple of years:

1. According to a post by DrJ, correcting something I “parroted” (mywords were about the classic 5deg improvement by using a bivy was my comment) as a reply some time ago, DrJ began with the word “Nope.” Then he went to say that bivy bags do NOT add to warmth. They protect from the wind and spray. Thinking about it, they do trap some air, but convenction is likely in that mass of air whenever you move or if a thicke layer of air exists anywhere (~1/4″ or thicker layer of air can have convection) and the bivy material itself is very thin and not a good insulator. Both quilts and sleeping bags can suffer from strong cold wind.

2. I’m not sure a WPB layer on the outside of a sleeping bag will weigh less than adding a 6.5-7.0 oz bivy sack, plus you don’t get any bug netting if that is a concern of yours. Check out MtnHw sleeping bags. Some of their bags come in DWR finish and some with their proprietary WPB Conduit SL laminant as the outer fabric. Notice the difference in weights. For example, a Phantom 32 with 10oz of 800-fillPower down producing 4″ of total loft weighs a Mfr claimed 21oz (i’m not sure of the length as the webpage is not real clear on this point). Compare this to their comparably temp rated Spirt SL 32 with 10oz of 800-fillPower down producing 4″ of total loft but weighs a whopping 41oz (again, not sure of length as the webpage is not clear on this point). That’s 20oz more. I suspect, but I’m only guessing here, is that the 21oz wt of the Phantom is a SHORT length bag (66″ I believe), and the 41oz wt of the Spirit is a regular length bag (72″ I believe). This is just a guess because MtnHW doesn’t clarify this and lumps them all together and many Mfrs (not sure about MtnHW) like to play marketing related “numbers” games.

At any rate even if the true difference is less than 20oz b/c there might be length differences, it would still come out to be much more than 6 to 8 oz for a DWR bivy. But then, the Conduit SL fabric is much more water resistant. It’s really going to depend upon what conditions and what type of shelter you’re using. A small poncho-tarp used in very wet/rainy areas may require a more water resistant bag or bivy.

3. If you layer a DWR bivy over a DWR sleeping bag, isn’t that better? I don’t know experientially, but layering a DWR layer over anything is better than not having one. So, my question is why wouldn’t two layers be even better than one? If a single DWR layer has some affect on keeping an absorbent base layer from absorbing water, then why wouldn’t it also have some effect on a second, inner DWR layer absorbing as much water? A company called TiGoat gives you the choice of a single or double layer top DWR bivy. There must be a reason. My guess is that it would improve the situation. In part, water pressure is responsible for driving water through some fabrics or causing wetting of some DWR fabrics (also length of water contact can come into play). If the first layer takes up the impact pressure of a water drop hitting it, then the second, inner layer has less pressure to deal with.

4. I use a lightweight bivy made of Epic by Nextec fabric. It is more water resistent than a simple DWR fabric, but is somewhat less breathable than a DWR nylon. I’ve yet to have my Epic fabric wet through, though I’ve NOT used it alone in all night downpours or mod-heavy rains since it is described as “highly water resistant under all but the most extreme conditions”. It’s difficult to quantify “extreme”, in my mind at least.

5. Montbell makes some highly water resistant and also GTX bag covers if you don’t need a full bivy with zip-out bug netting. Some are under 7oz in weight. Even pairing a 16-17oz Montbell GTX bag cover (again if you don’t need a full featured bivy sack) over the aforementioned Phantom 32 save 3-4oz over the Spirit SL version. Just a thought.

A non-waterproof bivy makes the most sense when you use a minimal shelter like a small tarp where you are not fully protected from the elements, wind and spray, as PJ said. It can be of help also to avoid drafts if you use a quilt. It also helps with the condensation that gathers on top of you because even if the DWR will not let it through (particularly if it’s condensing on you rather than dripping) part of it will still make it to the insulation when you stuff the bag no matter how well you shake it before stuffing. With the cover, even if it’s the same fabric as the bag shell, you avoid this as the humidity will be on the bivy, not on the bag shell. This kind of condensation is most common when you sleep under the stars.

Paul & Inaki–

Thanks for the insights. I hadn’t thought about the effects from stopping impact force and keeping water away from the bag while packed.

For reference, I’m also wondering about the benefits, if any, of using a dwr nylon topped bivy (as opposed to something more expensive) w/o a tarp on nights where there is little if any rain but condensation is likely to occur. Packing the water away from the insulation the next morning seems like a substantial benefit; I’m wondering what other benefits there might be.

Nathan, here’s what I’ve read on these Forums on using a tarp over a bivy. Camping under a tarp or some trees sets up a “microclimate” which, under certain atmospheric conditions, can tend to reduce condensation on the bivy where it might otherwise occur if the bivy were just placed out in the open, not under trees/branches by itself w/o the tarp.

I can’t think of anything beyond the obvious as I’m not a regular bivy user. As for bivy vs. tarp: small footprint, quickest setup time, night sky views… as for wpb vs. dwr bivy, the latter will breathe better but both will help with the dew. I don’t think it’ll be less expensive than a wpb one though