Are bivy sacks useless?

[Eric Carlsen]

Sorry for the hyperbole in the title, but I wanted to get your attention. I recently asked a large outdoors gear retailer about a down bag and whether or not it had a DWR coating. I mentioned that I was thinking of using a bivy and I didn’t want condensation to make the down useless. The person replied to my question, but then mentioned his experiences with bivy sacks.

He stressed it was just his opinion and experience, but he said he would no longer use a bivy. He said the condensation inside the bivy was too much for down, or even synthetic bags. He had tried some nice bivy sacks, he mentioned all of the new fabrics that supposedly offer superior breathability. But he found them all to be lacking.

I was thinking of moving to a bivy, but now I’m not so sure. I live in Ohio, which has very humid summers (although that’s because of the heat). I don’t know exactly the mechanism by which condensation forms on the inside of the bag, (is it just the temperature differential and moisture condensing from the air?), but I know we get a lot of dew also in the spring and fall. Maybe it’s not such a good idea? What experiences and advice do you have?

[Scott Peterson]

There is a wealth of info. on this subject within the board if you look around…and I for one am not an expert on condensation. My limited experience with a bivy though has left me with this: Even in rainy conditions (under a tarp), my silnylon bivy only had condensation as a result of my breath being enclosed. I zipped the thing up as ticks and large spiders were spotted immediatly around my camp and I wanted to avoid bites. I never have had the sweaty foot problem a lot of folks have. I suppose a mesh opening would have helped in this scenario, but ultimately I found the bivy in both wet and dry scenarios where I could sleep with it open VERY uncomfortable. It is very restrictive for my style of sleep. My suggestion is don’t overlook this facet of the gear. I have gotten so caught up in the scientific performance of a piece of gear that I overlook it’s practical usability. Make sure you get in a bivy before buying and do a reality check as to whether you think that is how you want to sleep during your vacation time.

[Christopher Plesko]

Perhaps i’m in the minority but bivy sacks are great for me and I don’t find them overly confining. I’ve used the emergency bivies with some minor condensation issues but the “high tech” WP/B bivy I have has been my only shelter on solo trips this past summer. I found it great over a wide range of temperatures and conditions.

[Glenn Roberts]

Hi, Eric. I’m also in Ohio, and do all my camping in Ohio, Indiana, and Kentucky (and some occasional trips to Isle Royale and Shenandoah NPs.)

I’ve always been a fan of bivy sacks, and never had any problems using them – until a couple of weeks ago. I was using an ID Salathe (which unzips to the waist and is fully backed by bug netting – a must for ventilation and bug protection around here), and awoke both mornings to find condensation inside my bivy, to the point that the sleeping bag shell had become damp.

I’d never had that problem with the Salathe before. But, as I think about it, I had never used a sleeping bag inside it in these transitional situations, either: mid-80s and very humid during the day, dropping into the low 60’s at night. Usually, on a hot, humid night I just slept with the bivy sack and no sleeping bag (think June, July, and August); the cold nights were usually also cool days with low humidity, and the bivy worked perfectly in conjunction with the sleeping bag.

I think it was just a combination of conditions that got me, but it was enough to help me decide that I’m going to stick with tents from now on – the convenience, coupled with weights (think TarpTent) that now rival or surpass those of the high-end bivies (like the Salathe or Unishelter) simply makes tents a better choice for me.

I’ve found the MSR Hubba to be a very good tent around here: all mesh body, lots of headroom, easy set-up, and a fly-only pitch that makes it simple to have a lunchtime shelter from the rain. I’m experimenting with a TarpTent Virga 2 (should arrive tomorrow), but I’m a little worried about condensation on a single wall tent. (Never had any such problems with the Hubba or my previous favorite, the Zoid 1.)

Don’t forget to include the weight of a tarp with the bivy. I’ve always found it necessary to carry a tarp to use in bad weather; the problem with bivies in the rain is that you still need to cook, change clothes, and get in and out of the bivy. Without a tarp, it’s virtually impossible to keep the inside of the bivy dry.

The Salathe weighs 2 pounds; an 8×10 silnylon tarp (the smallest size I found useful) weighs at least a pound, including stakes. Even if your poncho doubles as your tarp, the 2-pound bivy is the same weight as the TarpTent Virga 2. The tarp and bivy combo, at 3 pounds, is just a few ounces shy of the Hubba’s weight.

An excellent, light bivy (one pound) is the REI Minimalist. While it opens to the waist, it doesn’t have bug netting, making it somewhat warm to use around here. I coupled it with a Granite Gear White Lightning tarp (another really nice product at a pound and a half) to get a combination that weighed around two and a half pounds – which isn’t enough weight savings to make me give up the comfort, convenience and versatility of a tent.

In short, bivies can be made to work around here, but I don’t think it’s an ideal arrangement for our climate.

[Sam Haraldson]

Yes your bag will be a bit wet from condensation after a night in a bivy sack. You simply have to weigh that against how wet it will be if your bag is submitted directly to the splashing of rain.

I use a bivy under my tarp to fend off rain and as an extra layer of warmth. The next day when it’s dry enough out I simply hang my sleeping bag off my pack as I’m hiking and this airs it out enough for the sheen of moisture to dry from the bag.

[Mark Verber]

If you do most of your backpacking in the mid-west, I would recommend *not* switching to a bivy. Much of the year you will have high humidity and bugs are common for approx 1/2 the year. For the same weight as most full protection bivys you could get one of the ultralight shelters from six moon designs or tarptent.com and have more room to move around.

Of course, I am not a big bivy fan. The only times I think bivys are a prefered shelter is when you have extremely limited space to set up and/or very high winds. These are conditions more frequently found during alpine climbing than backpacking in Ohio.

If you do get a bivy, I would recommend one made from eVENT which breaths better than most of WPB materials and lets the water vapor exit in vapor state rather than needed to condense in the material before it is pumped outside outside the bivy as with most other WPB materials.

Mark… a former resident on Ohio.

Thank God I now have the sierras a few hours away by car.

[barry hitchcock]

i have a goretex double hooped bivi–i use it no hoops-one hoop or two depending on conditions—slept out one very humid night this summer- temperature 70f—slow moving lightening storm coming so set up with no poles or pegs — put everything i had made of metal 50 feet away from me–as soon as i got in i started feeling sticky and damp–so put one pole in –better but still damp legs–so two poles and dry as a bone

[J R]

I use a Bibler single hoop bivy (with the hoop removed) quite often. I DO notice condensation around the head area if Im totally zipped up, but with the hood open and the bug screen closed, its a very comfortable little bed. Plenty of room to move (yes, its heavier than some, but I never feel confined) and Ive never had condensation issues around my body… maybe thats because of the extra air space letting the moisture spread out a bit?

Anyway. I dont think a Bivi is useless at all.

[David Bonn]

With such an open ended question the only possible answer is:

All generalizations are silly.

Seriously, it depends a lot on the bivy, on the conditions you are hiking in, and a lot on you.

It is a real bad idea to wear wet socks or any wet clothes to be in a bivy, especially with a down bag. Better to let the wet socks hang someplace for the night and hopefully be less damp by morning.

The newer-tech bivys (like the ones sold on this web site) breathe very well in the conditions I hike in, and weigh less than a comparable groundsheet under a tarp (where I usually use the bivy).

I’m usually hiking in a much lower-humidity environment, and usually a heck of a lot colder, than most of the others posting on this thread.
Except for a brief baking period in July, most of my trips have involved quite a few nights in the low thirties, with around forty degrees being more typical. Plus a few hard freezes to keep things interesting.

[ian wright]

It’s been a long time since I used my gortex doubled hooped (?) bivvy but when I did I never noticed and condensation at all. I think the design is excellent.
But I think next time I travel I’d probably buy one of the new 1 person tents that weigh only a little more then my bivvy.

[David Lewis]

Here’s a question… whats the difference between a bivy and an overbag cover? When most people think of bivys… as sold by the big manufactures… they think of something with a hoop or two that is almost like a teeny tiny little tent… but in the ultralight world… what we call bivys seem to be little more than a bag with a string to hold it up off your head. Seems more like an overbag than what most people think of as a bivy. Is there a difference? Is it just than an overbag is (i’m guessing) not fully enclosed and therefore offers no bug protection?

[David Bonn]

Non-hooped bivys have always been pretty common, and are lighter and less expensive than hooped designs. The first bivy sacks I ever saw in the mid-80’s were non-hooped designs.

A lot of overbags are made of non-waterproof (or even water-resistant materials. If you dig around on campmor’s or cabela’s web site you should be able to come up with a few examples.

My problem with the hooped bivys (and I used one for several summers, in spite of the problems) was two-fold — there wasn’t any way to get in or out in a hosing rain without getting completely soaked, and their breathability was greatly reduced when water beaded up on the fabric or when the fabric finally wetted out.

The tarp and lightweight bivy and/or a bugshelter worked better (much better) for less weight than a hooped bivy. Just my experience.

[larry savage]

Bivy is of course derived from the word bivouac, a temporary open camp without a tent. Bivouacs, whether they are planned or unplanned are usually barely tolerable affairs.
Tied off to a little sloping spit of a shelf with huge exposure and a weather system moving in, feet jammed into your pack and everything you own on top of you, makes for a really fun night.
So of course we have bent the bivy bag to our sul needs and found it to be compromise. Every bag I’ve ever tried becomes an ordeal to dry your gear after a few days out in them. It is evidently the price to pay for adapting them. The miracle fabric in just the right conditions is always just around the corner while the compromise remains.

[Author]

Posts