Winter Bivouac Sack

[Takoda]

Manufacturers' claim that bivy sacks add 10 degrees of warmth to a sleeping bag. Any truth to this claim? Any bivy sack preferences?

[Booley]

Outdoor Research makes a good bivy. I have the Advanced bivy that is Gore-tex and is fairly breathable. Some condensation will occur in bivy sacks because of their tight fit/lack of ventilation. Of course the wider the opening the better. I double up with a lightweight tarp for more livable space. It's redundant but a good combo. Without the tarp, I've sat out some vicious storms without getting wet in the OR. Pricey but a good buy if you want one. I usually go to ground (hammocker) lower than about 35 degrees.

[bigcranky]

Two kinds of bivy sacks: waterproof/breathable (Goretex or the like), and windproof/water resistant (Pertex Quantum and the like). The w/b are heavier and really designed for climbers to bivy out on a cliff face (fun!). My hiking partner has used one several times during winter hikes, and had a LOT of trouble with condensation. In theory, your sweat and breath moisture can vent through the fabric, but in reality, that only works under very specific conditions. The Goretex style bivies are usually in the one pound range, but some are lighter.

The windproof/DWR bivies are *much* lighter, some down into the 6 ounce range. These are made from very breathable fabric, and are designed to block wind (which keeps you warmer) while venting body moisture. They are not waterproof, so you need a tarp, but they are water resistant enough for use under a tarp. (And you'll want a tarp anyway with a waterproof bivy -- think about trying to get in and out in a rainstorm.)

I have an older Mountain Hardwear breathable/windproof bivy. It's too heavy, but it does exactly what I want. It keeps the bag drier, keeps me on my sleeping pad, and the big mesh panel keeps the skeeters off my face. I have had zero problems with condensation. When I replace it, I'll make my own with a silnylon floor and a very light, breathable nylon top.

To answer the warmth question, the answer is, 'it depends.' Blocking convective heat loss is a big deal. My lovely wife was freezing in her 10-F down bag last April at Mt Rogers, though the overnight temps were only around 40. But there were gusts over 30 knots coming through our tarptent, and the heat loss was considerable. A windproof, lightweight bivy would have been a big help. But to imply that a bivy sack is the equivalent of additional insulation is misleading, IMHO.

Check out these:

http://www.titaniumgoat.com/Bivy.html

http://tinyurl.com/94arz

http://tinyurl.com/yb7lyv

Have fun.

[mweinstone]

i am the god of biviing. do not try to outbivi me. hokay,.....lets see. where to start?,......oh,... your dumb and im smart is as good a place as any. bivi=climbing/tent or tarp = camping. my bivi is a black diamond bibler winter bivi. 8.8 oz of epic .to use it in at conditions is to love to be clam.gabish? wet frosty clam.no bag likes to be in a bivi. now ive been talking about unsupported envelope style bivis. hooped bivies are tents and work fine on the at. but real bivi sacs as we climbers call them, are emergency use . and the hooped bivis being used on cliff face platforms are tents being used to biviwack on a sit that will not support a conventinal tent.biviwacking and the peice of gear called a bivi sac are two different things. the former means any unplanned sheltering without a conventional tent. bivi sacks are now split into two groups. those that are tents and pose no danger of condensation over extended use, and those witch are sacks and pose no condensation dangers over periods of short use.

and your not dumb.

[mrc237]

Used one on the PCT (1000 mi.) in 04' stayed nice n warm only had one storm and was dry throughout.