Bivy question

I enjoyed sleeping in my bug bivy so much I am now considering getting a regular style bivy for those cooler mountain nights. I don’t need a waterproof model, as my tarp does a good job of keeping off the rain. A breathable type nylon or other material should work nicely. Just something to keep the wind and bugs out. My concern is condensation. Is my sleeping bag likely to get wet from condensation inside a bivy sack? I would not think it to be much of an issue or bivy sacks would not be as popular as they seem to be on this forum. Thanks in advance.

Howie

Depends on the top fabric and any ventilation options. My hiking partner bought an Epic bivy from a cottage gear maker, and had *huge* condensation issues. He was basically soaked inside after one night. On that same night, sleeping only 20 feet away, I was totally dry inside my homemade bivy.

His bivy was made using the "standard" bivy pattern, which was designed for a waterproof mountaineering bivy. It has a slit across the chest for entry/exit, and a 4-inch wide strip of mesh across the eyes and nose. Once you are inside, there is very little or no ventilation, so all your exhalations are captured inside and cause heavy condensation. I also suspect that the Epic fabric is not very breathable. (He also sweats like I have never seen <grin>.)

My homemade bivy uses Momentum .90 fabric from thru-hiker.com. It has a huge mesh panel over the upper chest and head. There is plenty of ventilation, and yet plenty of protection, too, when used under a small tarp. I have a zipper that wraps around the outside edge from my right shoulder to my left hip, for ease of setup and entry/exit. The bottom is silicone nylon, for durable waterproofness.

I haven't tried all the commercial bivies, so I can't really comment, except to say: look for good ventilation. You don't need a full coverage, waterproof bivy (which you already know). Just something to add some weather resistance, warmth (in winter), and bug protection (in summer).

Check ebay often for a Mountain Hardwear Micromesh Bivy. It's about one third skeeter netting on the top and a taffeta type fabric from the waist down with waterproof bottom. When they show up they're "cheap" and all one needs under a tarp to keep the bedroll together and the bugs out.

The more I think about it, perhaps I simply need a light bag that slips over my sleeping bag but will fit nicely inside of my bug bivy? I only need a little wind resistance that is all. I don't plan on any winter trips. My wife is good at sewing, and with a little sucking up she might make me something <img src="/forums/images/graemlins/smile.gif" alt="" /> Can someone suggest a good material? What is the lightest wind resistant material available? Does wind resistance necessarily consititute being non breathable? Thanks.

Howie

What about the Weather shield from jrb? the pics show how to use it as a bivy


http://www.jacksrbetter.com/index_files/Weather%20Shield%20T2.htm

Or if you want to make one, and don't need the sil sides, you could have her "copy" it in a plain ripstop (or maybe DWR) nylon.

Ti Goat Ptarmigan. Nuff said.

I have an older style TI goat bivy that i really like, it is very light weight too. it is sil-nylon on the bottom and i believe epic on the top.

I have a bivvy with a "water resistant" top and coated bottom from OR that perhaps unfortunately, is discontinued. Condensation has never been a problem, and I've used it on some warm nights, cold nights, etc.

I hear that waterproof-breathable fabrics do vary significantly in breathability. I have an early Goretex knock-off tent that I don't think breaths well and sometimes has caused a slight problem (because tent is very very small).


For me, this factor is less significant in rainwear, but I'd want as much breathability as possible in a bivvy sack.

Unfortunately I can't remember the one everyone seems to prefer. Nextec? Epic? I don't remember......It's expensive whatever it is....The army tested various fabrics in their lab in Natick, Mass., and one came out on top.

Thanks for all your input guys. One thing I find is that I am quite often too warm and so I unzip my sleeping bag, and then during the early morning hours when it is quite cool I zip it up. It seems to me that with many of these bivys there is no side zipper which would leave me sweating a lot. I have been looking at the very light one by Outdoor Research. It seems like a good bivy, but where I live they are $144.00. It might be hard to convince the wife I really need it <img src="/forums/images/graemlins/smile.gif" alt="" /> I may have to wait for next year at that price. I seem to have exceeded this year’s budget for hiking equipment.

The mountains can be quite cool during late August. I may have to improvise for now by wrapping a poncho around me, or do what I did last year pitching my tarp in a more tent like fashion. The thing that really attracts me to a bivy is the fact that I have discovered I like sleeping under the stars. Pitching my tarp in a lean-to configuration blocks most of the wind and still allows me to do that. It makes me feel really free, not all closed in.

Howie

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