I'm redefining my winter shelter system for use in the White Mountains of New Hampshire.

To cut weight, I'm going to try using a shaped pyramid this year, but will also be experimenting with snow shelters.

I want a lightweight bivy sack that is:

Big enough to hold a Western Mountaineering Puma -25 sleeping bag and an exped 7 sleeping pad without compressing my sleeping bag and is also very breathable, enabling 2-4 day trips without condensation retarding my sleeping bag's effectiveness.

Any suggestions for winter bivy sacks that are big enough for my purposes and lightweight?

"enabling 2-4 day trips without condensation retarding my sleeping bag's effectiveness."

Not to hijack your thread but at temps around -20 does perspiration ever really reach the bivy. At temps way below freezing wouldn't the vapor condense and freeze before leaving the sleeping bag? So if that was the case then wouldn't a vapor barrier make a bigger difference in sleeping bag's effectiveness then how breathable the bivy is?

Ive never been out that cold so honestly have no idea but it seems like it would make sense.

I bought the Katabatic Bristlecone bivvy for exactly the same reasons. Loads of room for my Sawatch quilt and Exped 7 Downmat. It will be used in my Duomid. My TiGoat bivvy wasn't roomy enough.
I haven't used it at those temps yet though.

I would highly recommend you look at the MLD Alpine Bivy made using a 3L eVent top and footbox. I have Ron making a custom version which will have a 3L eVent bottom also, very cool.

That eVent bottom should prove superb at fighting condensation Thom. My ID all eVent bivvy has been the best i've ever used re condensation. I'm convinced the non breathable floor of most bivvys is to blame for a lot of condensation issues.
Bet it's pricy though.

I was in the Whites in summer but the weather was still challenging at times. I would recommend the ID all eVent Micro Bivy, it is roomy and WTB. I doubt if there is anything better available. I have a Bristlecone and agree that it is very roomy and can recommend it if that is more suitable when using a mid, the weight difference is not that great.

Mike,
The price upcharge was very reasonable for the upgrade IMO. If interested in a full 3L eVent Alpine Bivy contact Ron at MLD. I'm reluctant to provide pricing.

Edited by thomdarrah on 10/22/2010 11:16:07 MDT.

Mike -

Which ID all-event bivy do you have? I agree that an all event floor would be preferable over silnylon and given Ron's typical wait time for gear, using an ID product might let me get one earlier in the season, not to mention cheaper.

I'll be using this system with a Duomid and have been using an MLD Superlight bivy all season, but it's too small for winter.

if yr going to be using it inside a snow cave or a tarp ... do you really need event at those temps?

a pertex or similar one would probably be sufficient

I use this one Philip.

Thom,

Definitely looking forward to some specs and your thoughts once you receive and...especially...get a chance to test out your new bivy.

Mike,

You said your bristlecone was big enough for a quilt and an exped 7. How does the ID Overbag compare in size with the same bag or quilt/pad combo. Have you had enough experience with them yet to compare the two products? I am wary of compressing my down bag.

Also, why did you switch to the bristelcone from the ID Overbag? Was it the weight difference or something else?

I haven't switched bivvys Philip. They are both used for different scenarios. The Bristlecone/TiGoat bivvys are used when i carry the Duomid for backpacking, or expect to be under some form of shelter.
The ID bivvy is used as a 'stand alone' bivvy, often with a small head/torso tarp. I tend to use the ID bivvy for sketchy summit pitches and i tuck myself away into rocky niches where overhead shelter is difficult.

The ID bivvy takes the Exped 7 and my Sawatch with room to spare.

Edited by MikefaeDundee on 10/22/2010 11:55:20 MDT.

Eric,

Can you elaborate. I've had a lot of experience with eVent this year, but not much with Pertex, particularly in a bivy. Are you thinking about a certain bivy that uses pertex? What would the advantage be in colder temps?

I agree with eric that eVent may be overkill if you only want to protect against splashback. Of course, splashback will be non-existant at those temps.
I have no eperience of using VB gear.

Mike,

Glad I asked - thanks for the clarification. I understand. I am aiming for the tarp scenario only.

That said - how to the two bivies compare in sizing and breathability?

i suspect that something like pertex/momentum would breath better/no worse, be lighter, and be cheaper

the main advantage of event is if you wanted to use only the bivy ...

but with a tarp or snowcave .. i think DWR would likely be fine

the question is are you going to bivy out in the open in wet winter?

I can't compare breathability Philip, as it hasn't got cold enough to use the new Bristlecone that i bought for winter use. I've used the ID bivvy for a couple of years though, and it beats any Goretex bivvy i've used.Size wise, both are fine for me (5'10") with the Exped 7 and the Sawatch plus clothing. I guess about 4.5" of loft above me?
David Ure on this forum uses the ID bag(he put me on to it) and i think he is a tall guy, so he could probably give you more info on it re taller guys.

As you lay on snow, the snow melts. You will want a fairly high hydrostatic head to prevent getting your bag wet. DWR treated non WP fabric won't cut the bill. Event has a 10,000 mm HH. Event is as breathable but also fully functionally waterproof. I have never once (EVER) in a wide variety of conditions had noticeable condensation within my all eVent ID overbag.

Mike is right - I HAVE had condensation with another eVent bivy that had a non-breathable floor.

:)