bivies and bags

[Jarred_Jackman]

I was thinking if I just used my bivy and my sleeping bag inside of it, I might gain the extra warmth I want in the winter, while keeping the condensation off my bag. Has anyone tried this system as opposed to a warmer sleeping bag? How did it work? I'm just trying to think of all the ways to work with what I have rather than buying all sorts of shit for specific conditions.

thanks

[Cpt.Caveman]

Carry an extra down jacket.

[iain]

I use the bivy bag anyways because I gots me a megamid and I take the bivy bag on the mountain w/ me.

[cj001f]

I tried that last winter. It wasn't a success - I ended up with all kinds of water vapor condensing(and then freezing) in the insulation of my bag because the bivy sac wasn't breathable enough. I was using the MH Conduit bivy though, and it blows AnnaNicole style. I've heard that super breathable bags are the way to go (OR makes a sac in Dryloft that comes heavily recommended).

 

If your looking to add some range to your bag - try sleeping in dry Exp. Weight long underwear, with a hefty hat.

 

Carl

[mattp]

Many people routinely assert that a bivvy bag adds 5-10 degrees warmth to any bag. I've never owned a bivvy bag so I can't say for sure, but it is definitely my impression that these people are wrong and that condensation is a major issue with a gortex or similarly relatively unbreathable bivvy bag. For extra warmth, I sometimes carry an old synthetic overbag that I bought many years ago -- it was cheap because they are not in fashion and it is thin and cut roomy enough that it slips over my down bag. The condensation all ends up in this outer layer which is easier to dry than my down.

 

Wearing extra clothes to bed is certainly a good idea (contrary to the claims of Colin Fletcher who, in the '70's, wrote that wearing clothes in bed only made you colder and sleeping naked wast he way to go), and in particular I find that wrapping an extra sweater around my neck and shoulders helps reduce drafts even when I am using the hood on my sleeping bag.

 

Think about the ventilation on your tent or the drippage in your snowcave. Although the air temperature in a tent will be a little higher if you shut the windows, your bag will be completely covered with frost and, after a few nights, this will take it's toll on the warmth of your bag unless you dry it out each day by, say, running a stove in the tent or hanging the bag in the sun (huh? in the Cascades in December?). In a snowcave, be sure to carve the roof into a smooth dome shape so no drippage will get onto your bag.

 

Look also at your insulation beneath the bag. I find that whether I am sleeping on a thermarest or a ridgerest, an extra half length ridge-rest is well worth it and frequently makes the difference between a comfortable night and a wait-for-morning night.

[Toast]

last year I tried out a MH Conduit bivvy sac and experienced the same condensation prob you have. In fact, I was drenched the two times I used it. I returned the piece of shit to REI and exchanged it for an OR Basic Bivvy. Despite the sales guy's claims they're all the same, I didn't run into this problem with the plain vanilla GoreTex that OR uses, and I've been quite happy with it.

 

As far as warmth, I do think it moves you a notch up in insulation. I'll need to test this out with my light down bag this weekend in winter conditions. It did jus fine in spring snow.

 

As far as sleeping systems, I was always cold with a thermarest on snow until I started adding a closed cell foam pad to supplement it. Can anybody comment on the merits of two closed cell foam pads vs. one and a Thermarest? I'd just like to lighten things up a bit.

 

 

[mattp]

I mostly prefer the double ridgerest because it is lighter and will not fail by develping a leak. However, it is bulkier and while this is not an issue for most general mountaineering, it can be a concern on technical climbs and when bushwacking. A thermarest/ridgerest combo may be slightly warmer and more cushy, though, and you don't look like quite such a bozo with the big bulky pack when your pals packs are smaller.

[Minus]

My experience has been that so long as the bivvy bag is kept propped away from your face (rucsac in hood area works ofr me) and you've left a little hole for ventilation, condensation isn't too much of a problem.

My bivvy bag is a Mountain Range goretex bag. Probably can't get these overe here but try needlesports.co.uk and go from there.

[AARON1]

Has anyone had a chance to use the Bibler Tripod Bivy?

[Beck]

a couple comments about bivy sacks/foam pad issues.

 

Yes, carrying a second closed cell foam pad, half to three quarter length, is beneficial in a couple of ways. 1: you can widen your sleeping footprint a bit to allow for some toss and turn 2: you can use one out of the snowhole, and have your bag on one inside, lofting up while you sit in comfort while making dinner. 3: and most important to me, you can use the two pads like a mini dryer by sandwiching gloves, socks, coat, shell pants between the two, it keeps them from freezing solid overnight. putting on frozen mitts in the AM is not a fun prospect, keeping them between the two pads also increases your insulation from the snow (where you will lose more of your heat if you are inadequately insulated below you) carry a light ground sheet to use as a floor for snowhole or tarp tent to help sort gear, and keep drier.

 

 

As to bivies Vs. synthetic overbags, or just a warmer bag.

All waterproof bivies will condensate on the inside. The fabric does not have a high enough transpiration rate. But it is usually manageable for a couple days in down. Longer trips, you need to rethink the system.

 

Adding an overbag, like Mattp is suggesting, keeps your inner bag drier for two reasons- the outer bag will grab the moisture from outside, and keep it off the inside bag, and also, the dew point where your perspiration vapor condensates as liquid is now moved OUT of your inner, down bag, and into the outer bag. Moving the dew point into the outer bag keeps your transpiration in a vapor state, and moving through the inside bag in a vapor. This is preferable to just buying a warmer down bag.

 

The new encapsilated nylons found in some sleeping bag shells will provide great weather protection, but you still have the dew point in the bags' insulation if you just carry one, heavier sleeping bag.

 

As to styles of bivy.

the OR bags are tight, the bibler and integral bags are more roomy. I use a Bibler big wall in Long, it gives me enough room to store some gear inside, boots in the foot area, gear alongside me for added insulation, and the hooped area is big enough to read a paperback book in or eat some snacks (as long as you know there are no snaffles around!)

 

The first Bibler tripod bivy i checked out was a POS, the poles were so taught in the pitch it looked like the damn thing was gonna blow, plus the foot hoop wasn't very secure in the foot area.

Better might be the bibler Bipod, but as stated earlier, the standard hoop bibler bivy gives you enough room to read and eat.

 

Oh, ya, and don't zip yourself up all the way into a bivy !

[Smoker]

I think that some folks naturally produce more "vaper" than others. On extended trips this will be more of an issue.

 

For a night or 2 out, if your having condensation problems it is a gear issue IMHO. Leave room for off-gassing by not sealing your self up tight. On multi days out I make use of the wind and thermals to "air out" and dry my bag. I heard somewhere that it helps to roll your bag up tight (2tx) as soon as you exit it to force as much of the warm air out and reduce condensation build up.

 

I carry 2 ridge rests, full & 3/4 for winter temps for insulation and wear as much clothing as I can/need with out restricting loft. I have been cold but never too wet.

 

I bought a great biv sac from LL Bean many years ago. Interesting thoughts on the overbags ability to transmit vapor.

 

If all else fails grab your and pray for daybreak.

 

Oh yeah, last time I was smoking in the Muir Hut (week after x-mas a few years back) I brought my Biv and summer bag and single full length pad. Ice box cold in that stone but I slept warm Biv sacs do add warmth.

Edited December 20, 2002 by Smoker

[Dru]

Buy an overbag if you waant your bag warmer. all the condensation will occur in the overnbag so get a syntho one and it willkeep your down bag dry.

 

The warmer bivi bag thing is cause it blocks heat loss from advection. Its warmer compared to sleeping in the open, i guess, IE its warmer than sleeping without a bivi bag. But its not any warmer than being in a tent, and I wouldnt say it really adds any +5-10 degrees to your bag. If a bag is too cold it will be too cold even with a bivy bag over top.

[jordop]

I prodealed a Mtn Hardware Conduit job and it totally sucks for vapour dispersion as the bottom, like most bivy sacks, is PU coated nylon. THE BEST WAY TO GO is with MEC's emperor Penguin overbag as the whole thing is Dryloft and the synthetic layer will wick most H2O out of a down bag. Mind you, it can't stand in for a tent like the Integral Designs unishelter, which I have found is actually quite useful here and there.

[cj001f]

The warmer bivi bag thing is cause it blocks heat loss from advection.

 

?Dru, praytell what is advection? Cooling by commercials?

 

Condensation amount veries alot w/temperature. I found I was relatively condensation free w/ the bivy sac to nightime lows of -5F, but below that, even with keeping the bag away from face, etc. I built up a massive amount of precipitation.

 

It's not just the bottom of the MHConduit's that don't breath - it's the top too. Has to be one of the biggest ripoffs around.

 

 

[allthumbs]

ad·vec·tion

n.

1. The transfer of a property of the atmosphere, such as heat, cold, or humidity, by the horizontal movement of an air mass: Today's temperatures were higher due to the advection of warm air into the region.

2. The rate of change of an atmospheric property caused by the horizontal movement of air.

3. The horizontal movement of water, as in an ocean current.

[iain]

my bivy sack has the dubious nickname "The Odor Pod"

[allthumbs]

thanks for sharing Iain

[cj001f]

Grazie, trask.

 

Meteorologically then, convection is air motion upwards, and advection is motion sideways?

[allthumbs]

If you say so.

[fleblebleb]

I'm getting a 40 degree 1 pound down bag as soon as I can afford it. I already have a down parka, a 20 degree synthetic bag and a bivi bag so I figure I'll have lots of useful options for mixing things up. Parka plus down bag plus synthetic bag plus bivi bag will be way warm together, too warm for almost anything in the PNW.

 

I've been using my synthetic bag with the parka and bivi for winter and snow trips, works great except my feet and legs sometimes get a little cold. However, I only get condensation around the bag openings - not in the footbox. When I use the same combination minus the parka in summer I always get condensation in the footbox too.

 

 

[Greg_W]

flebbie - I am thinking of the same set up: 30-degree down bag with bivy and use an insulating layer if necessary. Nice, versatile, and pretty light.

[allthumbs]

Greg, you and Fleb should read this shit first.

[Greg_W]

Already did. I like what I've seen/read of the Western Mountaineering bags; Pro Mountain Sports has 'em.

[allthumbs]

Yeah, I know why you like their shit.

[Greg_W]