I'm seeking some advice regarding condensation problems I keep having with my sleep system. I'm using a Nunatak Arc Alpinist in a BMW Vapr Bivy. For padding, I use a Gossamer Gear (GG) NightLight torso pad and my empty pack under my feet. I supplement with a 1/8" GG ThinLight in cold weather.

Last night I was out in the Smokies with temps about 18F around 5000ft elevation. I was sleeping in 200-wt fleece pants, a BMW Cocoon, and a fleece balaclava. I was comfortably warm early on in the evening, and nowhere near overheating. As the night progressed, I ended up with puddles inside my Vapr Bivy all along both sides on the sil-nyl bottom. This of course soaked the edges of my bag and led to significant discomfort. Ironically (and amazingly), the Golite Hex 3 my friend and I were using for shelter actually had zero (and I really mean zero) condensation in the morning.

I've actually had the same condensation problems in my Vapr under a variety of weather conditions and have essentially concluded (unless someone can help), that the bivy approach will just not work for me. Unfortunately, I think I have more of an issue with insensible perspiration than most. When I used to use a traditional synthetic bag and a z-rest, I'd almost always wake to little puddles in the z-rest dimples regardless of weather conditions and shelter type (bivy, tent, tarp, shelter).

Any thoughts or suggestions would certainly be appreciated.

Regards,
Jeff

That's interesting you say that. The first weekend in Nov, bp in Dolly Sods with night temps around 20*, I had the same problem using my BigAgnes down Horse Thief sleeping bag inside the BMW VAPR bivy... water puddling along both outside edges along the inside of the bivy and therefore soaking the outside edges of my sleeping bag. I would bde interested in responses also.

One more piece of info. I was using my bivy under a GoLite Lair 1 tarp and there was no rain that night.

I've had the same problems using my Vapr Bivy under a SpinnShelter on a cold and foggy October night following two days of torrential rains. My MontBell UL Downhugger was soaked along the edges in the morning. And I kept sliding on the silnylon off toward the head end of the shelter because the ground was uneven... (no other place to camp in the very crowded official campsite due to strict regulations in this particular national park in Japan on off-campsite camping). I keep trying to figure out how this system works for others... surely I must be doing something wrong. Do others find that painting silicon onto the silnylon helps? (I'm loathe to do anything to such an expensive piece of gear unless I can be sure it will help). And how do others deal with the condensation?

Miguel,
Hate to tell you this, but bivies tend to have more condensation than you would expect. They have almost no ventillation in the foot area and the shell stays cold if your sleeping bag is doing its job, so there is little heat to keep insensible perspiration in vapor form to pass through the shell. This problem has been around forever, ever since waterproof/breathable materials have been used for bivies. You may have noticed that even in a tent your sleeping bag gets wet just under the outer shell. Same reason. Water vapor migrates through the layers of insulation, cooling as it reaches the outermost layers, then condenses inside the shell. When you are in a bivy, you can actually see the water. The tighter the bivy fabric, the more likely you are to get condensation. My old first-generation GoreTex bivy was really bad about this, so I dumped it. The only solution is to vent the bivy as much as possible. A longer zipper may be in order and perhaps a drawstring foot with a spindrift collar to keep rain out.

RE your next question, consider adding stake loops to the bivy. If the bivy itself is sliding, you can nail it in place. If *you* are sliding on the silnylon, consider putting stripes of silicone sealant across your sleeping pad - not the bivy floor. If silicone will not stick to your pad, try other types of sealant or liquid rubber - including polyurethane rubber sealant. The sleeping pad is much less expensive than the bivy, and you will avoid hurting the resale value of the bivy if that matters to you.

Do you think the reason is because the silnylon "bathtub" floor comes up a little too high on the sides? Individual perspiration must be considered but that might be ruled out if it happens to enough people.

Many bivys do have WP bottoms that come too high up the sides. I think it contributes to the problem.
Foot area condensation is an issue as Vick points out. One of the reasons I like the MLD bivys (Soul Bivy, anyway)--- they have a drawcorded foot section. You can open up the bottom all the way for ventilation and temperature control or cinch up tight in the worst conditions.

Has anyone had similar problems using just a ground sheet (no bivy)? Obviously, there'd be much more room for evaporation of the moisture, but would there still be pooling along the edges of the pad/ground sheet interface?

Jeff

Hello All.

First, the BPL bivy's are fine products.

Second, all bivys of any fabric or design will condense inside in certain conditions, MLD ones included.

My feedback from customers, my 25 year+ personal experience and from reading posts and info from many sources is that this is part of bivy life.

Some products are better than others. Some people fare better than others in the same product.

The only two factors in the bivys themselves are fabric selection and design.

Most of the UL and SUL bivys that use Silnylon, Nano, Cuben, SpectraLite(MLD comming in the Buddha Bivy), PU coated or other various totally waterproof bottom feature a simililar design of the bottom wrapping up the side. Most have the bottom girth match the top girth. This is because it is easier to build and so costs less. The roll widths of the fabric yeilds two bivy tops for a given length instead of one. The silnylon bottom is less expensive than the top. Maybe the new .5 stuff is the same or slightly more than the top fabric.

A more shaped top that would wrap down the sides farther require either a wastefull boxy/simple head and shaped foot design or more sewing and shaping. -More expensive.

The top fabrics are what they are...Pertex, DWR nylon, Epic, eVent, Gortetex or a range of other PU /Acrylic coated fabrics. Most are pretty good. More of it than the coated bottom will help some, but don't look for the holy grail of zero condensation. Obviously the more breathable the less condensation but it's a trade off with protection.

I have started to use less of the bottom material and more of the top. Instead of a 50/50 it's now closer to 65/35. One part than seems to make a difference is in the head torso area. More brethable there helps a lot more in percentage than in the lower part. makes senses as there is a lot more skin area to persprire. In my newest bivys the foot is still at 50/50 and the head more like 70/30 with the top of the head almost all breathable. I also use a drawstring foot for ventelation and since the top has a wider girth, the zip opening is wider and offers a wider vent.

A lot of designs are possible but I wonder if the market, which already has $250+ (under tarp) bivy's can support more design.

Weight is also an issue. At some point , for many, the weight became the holy grail of SUL as opposed to pure function. If the bivy can save an ounce of condensation or time to dry it, is it worth it? Tech exists to make sub 1 oz bivys but the function would be pretty rough.

Your feedback and open debate on these issues help drive companies to do better and we all owe BPL a debt for providing the forum. Thanks Ryan.

Jeff,
Sometimes you get condensation inside the sleeping bag, no matter what, bivy or no bivy. Condensation on the ground sheet is less common since warm air and its load of water vapor tend to rise. But bivies have more problem with condensation than sleeping bags alone.

I've always wondered why it is that so many animals can sleep warm and dry without all the fancy gadgets that we use. How do ducks, for instance, manage to sleep in frigid winter lakes using just their layer of feathers and a coating of oils to protect them from the heat leeching effects of the water?

The only raingear that I've ever used that truly never has any condensation inside is the Paramo ( http://www.paramo.co.uk/UK/index.html ) Cascada jacket I have. Paramo is a company in Scotland and few people outside the UK know about their gear. Using their better known Nikwax products to treat the garments in the same way ducks treat their feathers and sea otters treat their fur, they have developed a system based on the way animals stay warm and dry, rather than using barrier systems as everyone else seems to be doing (it doesn't work the same way as pertex/pile garments... if the pertex/pile garments are treated with the Nikwax solution their performance drops significantly I've read). The whole idea works on the idea of drawing water away from the body, and less so in preventing the water from permeating the fabric (though the Nikwax solution provides a temporary DWR finish that you have to wash back in). If a tear develops in the fabric you can sew a patch on right in the field with no loss of performance in the system. The idea is quite counter-intuitive, but amazingly it really works. It seems there are a lot of people who either love or hate the system. I personally find the Cascada jacket near perfect... it's just that it is a little too heavy. If Paramo could figure out an ultralight version of their idea it would be a hit.

I'm wondering if this system can be used in making a bivy... the condensation problems would be solved, I think.

Bivy condensation is why I moved to a longer homemade tarp without bivy. I wish the tarp makers would make their tarps longer.

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Edited by butuki on 12/18/2005 21:24:03 MST.

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Edited by butuki on 12/18/2005 18:25:13 MST.

Not sure why the post keeps repeating itself. Only posted once... I've been trying edit out the extra posts but they keep returning... Sorry about that.

I have found that condensation insdie the bag can be eliminated by use of a vapor barrier shirt, like Stephanson warmlite makes. The shirt is amazingly warm byitself. The warmlite website has a whole explanation about relative humidity inside the shirt preventing the loss of moisture from your body. Maybe that's true, but the combination of the vapor barrier shirt, an old 20 degree bag have kept me warm and dry on many very cold and windy nights. The shirts do not make you clammy. They are also waterproof and can be used to hike in in the rain if the temparature is correct. They have a lot to say about condensation in tents as well.

Tim,

I don't understand this wish... There are a whole bunch of differnt size tarps readily available... light too... I do understand you point on eliminating the bivi...In fact the weight of a more reasonable sized tarp ( say 8x8 at 9.4 oz) in silnyl would be lighter than an absolute minimum tarp and bivi in nono or cuben and a whole lot less cost... if warmth, however is the issue a breathable bivi still adds.

8x8 at 9.4oz... I wonder who makes a tarp like that. But, the square shape has never grown on me for general use. Just doesn't 'feel' right, hammocking excepted.

Tim, I do understand your wish. A bit taller than average, the standar 8' length isn't really convenient. I'd gladly give up some width for a few more feet from head to toe. Etowah Outfitters [Georgia] makes a 6x10 siltarp at 9oz. Might be worth a look.
-Mark

Mark check out the Gossamer Gear SpinnTwinn tarp.

http://www.gossamergear.com/cgi-bin/gossamergear/Spinn-Twinn.html

Weight:
· 8.0 oz - Tarp before seam sealing
· 0.4 oz - Stuff Sack (included)
· 2.0 oz - 8 6” Titanium stakes (recommended)
· 0.4 oz - 25’ of EZC Orange line (included)
Size:
· 47 sq. ft. - Complete tarp area, staked down position, not counting entrance overhangs
· 120" - Length of tarp ridgeline
· 110" - Total width of front of tarp (55" per side)
· 86" - Total width of rear of tarp (43" per side)
· 12" - Front entrance overhang
· 6" - Rear entrance overhang
· 102" - Wall length at ground level
· 44" - Height at peak with 45" pole (can increase with pitching options)
· 67" - Front entrance width, using 45" pole, tarp staked to ground
· 62" - Rear entrance width, using 32" pole, tarp staked to ground
Price:
· $134.95

Edited by FastWalker on 12/19/2005 09:29:47 MST.

Mark,

Here is one place to find such a tarp.

http://216.83.168.206/index_files/Products%20List_files/8x8%20SilNyl%20Tarp.htm

Note. as owner, designer I'm biased.