Best Lightweight Bivy to Protect a Down Bag

[Roland Fein]

It appears this is the best place to ask this question. I have just made my first leap into down bags for the world I play in, which to many is very taboo as its quite wet here in Alaska. My question is can someone reccomend to me what the lightest yet breathable bivy bag is to protect a down bag while sleeping in a shelter in a fairly wet environment.Thanks

[D L]

Not sure that I am the best authority on this as there are those on this board that utilize bivys far more than I do. My take: if you are going to be in a shelter or under a tarp and all you need is a bivy to protect your down bag from spindrift, occasional splashes, and some dripping, then you could go with anything, maybe even down to the BMW nano bivy which is really nothing more than another pertex shell for your sleeping bag. I would probably go for at least an epic shell to be safe (TI Goat), though. If you are going to be only minimally protected by a tarp and may even be sleeping somewhat in the open or where the precipitation might shift directions leaving you exposed, I would go with a stormproof bivy made of a completely waterproof material. My recommendation would be eVent (Mountain Laurel Designs). Having said that, I can't really ever recommend sleeping in a bivy without some sort of accompanying shelter unless you are going to be in a completely dry environment. All it takes is a little bit of dew to settle on your bivy and your otherwise breathable bivy is no longer very breathable and your sleeping bag may get wet from your own condensation. I live in the Pacific NW and this has happened to me several times. I have a WM bag with a Pertex shell and so far it hasn't been too bad because it's only happened on overnighters. If I were on a longer trip with no time to dry out my bag it may have been a problem.

[Jason Brinkman]

Tough to answer your question without knowing the specifics of your "shelter".

If you need truly waterproof and highly breathable you probably want eVent or Pertex Endurance. You will pay a weight penalty for both. You weren't specific on what "shelter" you would be sleeping in, but for most a DWR finish on Pertex Quantum or similar would be sufficient for drips and spindrift. If you are in a smallish tent where the biggest risk is touching the ends of the tent, then a waterproof shell on the sleeping bag itself could work. Probably a little late if you've already invested. Golite is making bags now with only waterproof ends and more breathable midsections. Bivies work for extra insulation too, especially if it's windy in your shelter.

[Jason Shaffer]

For very wet, cold weather I use the MLD Soul bivy (Momentum 90 top and eVent foot panel) combined with a big cat tarp, or even a pyramid. I've found Momentum 90 to be as breathable as Pertex Quantum, but slightly more rain-resistant when new. Being water-resistant rather than waterproof, it is noticeably more breathable than eVent.

I would avoid eVent for any bivy used with a tarp. It is not breathable enough to mitigate internal condensation effectively in cool humid conditions. To increase the resistance to external moisture, beef up your tarp, but keep your bivy as breathable as possible.

[David Ure]

nm

[Andy Dixon]

I too have a heavily used eVent bivy where i have never experienced ANY condensation even though I often used it in cool & humid conditions.

[Jason Shaffer]

OP said ‘lightest, most breathable bivy’ for use with a shelter. Momentum 90 and Pertex Quantum are more breathable than eVent. Also the MLD Soul and LiteSoul are 7 and 4.4 oz respectively.

David, Andy : That’s interesting. I don’t discount that at all. Our experiences might differ in a few ways…

Three days, meaning two nights? Two nights isn’t a lot of time for condensation to accumulate visibly in either bivy type – maybe in extreme cases. Also, 38F low isn’t especially cold when it comes to really bad condensation issues, IME. Anything much over 40 this is usually a non-issue.

Up to a week of foggy sleet, 35-45F much of the day, lows to 20F … that’s more what I was thinking. (Maybe Roland can clarify.) It’s just been my experience that a more breathable bivy prevents condensation buildup better than a fully waterproof bivy, over multiple nights in this kind of weather. Maybe this is just a personal-preference thing. But I’m interested to compare notes…

[Damien Tougas]

Although I don't own one, from what I have read the Oware (http://www.owareusa.com/) bivys are supposed to be quite good. They are made from EPIC and silnylon and therefore should be light, very water resistant, and breathable.

[Monty Montana]

Hi Roland, welcome to the club! I have only used down bags, started experimenting with bivys about a dozen years ago, and in the process became a devout adherent. This was before I discovered the ultralight movement. Because the weather in the PNW is similar to yours in Alaska, what I learned through trial and error will be applicable.

* Breathable is better than waterproofness in most shelter situations for an ultralight bivy.

* WP is the gold standard in more exposed situations for a heavier storm bivy.

* For cold weather, weather approaching the dew point, or prolonged wet weather, use a vapor barrier liner! This can not be overemphasized for down bag use, as it will slowly start to wet out from insensate persperation; a VP liner keeps this from condensing inside the bag.

* And don't breath inside the bag! If the air is cold enough to require preheating, adjust your balaclava so that it pre-warms the air for you.

For more information, get the Bivy Sack Review from the print version of Backpacking Light magazine, vol 7. In it 14 bivys are evaluated for storm protection, insect comfort, condensation resistence, packability, livability, durability, weight, and cost. At different ends of the scale, the Equinox ultralight and the Oware Epic came out tops.

Happy Trails!

[Dug Shelby]

Has anything changed since 2008?

[Richard Mock]

or 2013

[Håvard Skarping]

or 2015?

[Dylan H]

I don't have experience with some of the bivys mentioned earlier in the thread, but I just invested in a SOL Escape Bivy. I have yet to use it on a trip, but from the research I did before I bought it it isn't the best, but for the weight and price it works well. (And I got a great deal on it)

[Franco Darioli]

The reason why many in very cold areas ,like Alaska, don't use down bags it isn't because they worry about getting them wet from the outside but because they get them wet from the inside (perspiration)
That is OK for a day or two not so much when they become solid after a few.

[Doug Hus]

I really like my MLD -Superlight- under a tarp / shelter. http://www.mountainlaureldesigns.com/shop/product_info.php?cPath=22&products_id=30

Doug

[Lizz Roe]

Hey Dylan you were going to use the sol escape bivi ona trip have you done so yet and what was it like? Was it the really teeny packed one or the new breathable waterproof one? Ive got both but haven't used them yet – weather is too crap at the moment in Wales…

[Author]

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