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is bivy bag or over bag best to cover down sleeping bag?

is bivy bag or over bag best to cover down sleeping bag?

Personally I like a Bivy bag as the last one I used had a hoop over the head to keep that section off the face.

Depends...

BIVY BAG-> good for snow caves and quinzees to keep bag dry

(light) OVERBAG-> good for absorbing moisture from main bag on multi-day trips. Body moisture condenses in the cooler over bag. A light over bag is able to dry much faster when hung out. Also gives more warmth than a bivy bag.**

** Overbags should have synthetic fill like Climashield or DWR treated down so they dry fast.

I left active duty in the Marine Corps right before all the great gear-Gore text parkas, better boots, GPS units, improved sleeping bags and bivvys were issued to ground combat units. I acquired a North Face discontinued bivvy about 12years ago and found it useful to add 10 degrees of warmth to a bag. Rode out a few rainstorms, but got wet in the NF bivvy. Acquired a USMC bivvy a few weeks ago and rode out two storms dry as a bone. The military bivvy didn't have the headroom with overhead wands, but no water came in.

I have used a BD Winter Bivy, which is just a very light cover with a chest zip and no longer made, plus an MEC Emperor Penguin overbag. This combo is a pain to get in and out of because of the BD chest zip. I now have a warmer bag and may leave the overbag at home next time. I'm not a big fan of bivys because many of them weigh as much as a small tent and I'd much rather be in a tent, especially if it is snowing or raining. Nothing like a tent in cold weather in spite of dragging it along (sometimes literally with a sled, I may have some pics posted here somewhere from a couple of years ago).

I agree with Tom. In wet weather, better off with a tent and no bivvy.

what are you trying to achieve?

Protection from external environment?.... or just adding more insulation?

winmag and TJ1984 really covered it all. Bivy bags and overbags have different purposes. And like every other category of gear, some models do what you want better than others.

The type bivy that Tom mentioned is best suited for an emergency (or planned) bivouac. You know there is a possibility (or plan) to stop part way on a climb or trek or might be encountering a storm. These mostly are a windshield, keep off the main part of a snow or rain storm, and add maybe 5 deg warmth. So a simple bivy is hauled out of the pack, you get in, scrunch up on a platform and rest/sit out the night/storm, etc.

Then there are bivies that are a bit larger volume and have a hoop at the head end. Not quite a minitent, but better ventilated. they may add 5-10 deg warmth and may keep you a little drier. Integral Designs made a couple of versions of this - excellent for ventilation, minimal condensation. Unfortunately, when RAB took over ID, these all vanished. Minitents are similar, basically a tiny 1-person tent (leave your gear outside). They are still, like all bivies, an emergency shelter (though I have used them as a tent substitute intentionally). There are also 1-person tents, with plenty of room, good ventilation, but a bit heavier than the 1-3 pounds of a bivy. There are lots of times I use my Hilleberg Suolo. It is expensive, though.

Overbags are simply added insulation to add warmth. They do move the "condensation zone" farther out.

So, to quote TJ, what is your goal?

December 5, 2020
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