Winter Bivy Sack Guide

Winter Bivy Sack Guide

Winter bivy sacks were first developed as solo shelters for mountaineering and climbing where participants were interested in lightweight and highly compressible gear. The biggest advantage of a winter bivy sack is the ability to use it anywhere you want to stop and sleep, be it a rock ledge on the side of a mountain, a snow cave, or a shallow ditch you stomp out in the snow to protect yourself from the wind. They require no tent stakes or tent poles and they pack up very small which is an advantage when you want to keep your winter gear lightweight and compact.

Most winter bivy sacks are made with waterproof/breathable top fabrics to help reduce internal condensation and waterproof base fabrics to keep your sleeping bag and pad dry. In some cases, hooped tent poles have been added to winter bivy sacks to making them more livable in stormy or inclement conditions when you need to stay in them for a longer period of time. Insect netting is also available in some cold weather bivy sacks and can be useful when they’re used in spring conditions.

Make / ModelWeightW/B Top FabricPrice
Black Diamond Twilight Bivy10 ozNanoshield$150
Black Diamond Spotlight Bivy17.6 ozNanoshield$220
Black Diamond Big Wall Hooped Bivy26 ozToddTex$240
Mountain Laurel Designs Event Soul Bivy12 ozEvent$255
Mountain Laurel Designs FKT Event Soul Bivy10 ozEvent$225
MSR E-Bivy7 ozRipstop Nylon$100
MSR Pro-Bivy10 ozRipstop Nylon$200
Outdoor Research Stargazer Bivy18.9 ozAscentshell$259
Rab Survival Zone Lite Bivi8 ozPertex Quantum Pro$155
REI All Season Bivy27 ozEvent$229
REI Shell Bivy19 ozRipstop Nylon$149
Sierra Designs Backcountry Bivy13.5 ozRipstop Nylon$160
The North Face Assault Futurelight Bivy 15 ozFuturelight$169

Advantages of Bivy Sacks

There are many advantages to sleeping in a waterproof bivy sack over a tent. It is easy to find a place to put a bivy sack at night since it only requires as much space as your sleeping bag and sleeping bag or quilt. Simply unroll your bivy sack, slip your sleeping pad and sleeping bag inside.

Bivy sacks can be set up just about anywhere without the need for tent guylines or stakes
Bivy sacks can be set up just about anywhere without the need for tent guylines or stakes

There are no guylines to set up and tent stakes to freeze into the ground so you can get inside without delay and get warm. Being waterproof, you don’t have to lie on top of a groundsheet either, since the bottom of a waterproof bivy sack is designed to keep you dry. Bivy sacks also add a few degrees of insulation to your sleep system.

But two of the biggest advantages of waterproof bivy sacks are their lightweight and packability, compared to a tent. These two properties are important for climbers, cyclists, adventure racers, and fast and light hikers who want don’t want to be weighed down and want to bring as little gear as possible. Bivy sacks also make great emergency shelters for solo winter hikers, provided you carry a sleeping pad and enough insulation to get through the night.

Disadvantages of Bivy Sacks

Bivy sacks are much more confining than tents, with only enough space for you and a few small personal items. Your backpack and the rest of your gear will be fully exposed a night without any cover. Bivy sacks are also more prone to internal condensation than a tent, even when manufactured with waterproof breathable materials. You’re best off keeping them open or unzipped at night to maximize air circulation and ventilation in order to keep your sleeping bag/quilt dry and condensation free.

How to Choose a Winter Bivy Sack

Here are the key considerations to weigh when choosing a winter bivy sack.

Waterproof/breathable top fabric

Having a waterproof/breathable top fabric is important to vent water vapor and help minimize internal condensation that can make your sleeping bag wet. However, unlike rain jackets, most bivy sack manufacturers do not list the laboratory measurements used to rate waterproofing (hydrostatic head, abbreviated “HH”) or breathability (movable water transmission rate, abbreviated “MVTR”). That can make expected performance comparisons between different bivy sacks difficult.

That said, winter bivy sacks made with Gore-tex or Event are significantly more breathable (often by a factor of 2 or more) than bivy sacks made with the proprietary waterproof/breathable knock-offs like Black Diamond’s Nanoshield or the North Face’s Futurelight fabrics. They generally cost more, though.

More headroom

If headroom is important to you, consider getting a bivy shelter with an interior pole. These bivy sacks come with a flexible fiberglass pole that slides into the hood area to create more volume around your face and shoulders. The tradeoff is that they tend to be heavier than more minimal bivy sacks.

Entrance and exit

It’s much easier to get in and out of a bivy sack that has a zipper along the side than one that only has one at the head end.

Insect netting for warmer temperatures

If you plan to bivy in early spring when biting insects emerge, make sure to get a winter bivy sack with a mesh panel over the face so you can sleep without insects biting your face at night. If you only plan to sleep in a bivy sack in winter or in snow caves, a mesh panel will be less important. For warmer weather use, I’d encourage you to invest in an ultralight bivy sack or bug shelter rather than a winter bivy sack, since they’re much cooler to use. See our 10 Best Backpacking Bug Shelters for our recommended warm weather bivy sacks.

Weight and Packed Size

Don’t forget to consider the weight of the bivy sack and its packed size, since one of the chief benefits of using a bivy sack is gear weight and size reduction. There’s often a tradeoff between features and weight/size, but some winter bivy sacks are surprisingly lightweight and compressible.

Sizing and Fit

When in doubt, order a bivy sack (check the retailer’s return policy) and lie in it at home to see if it fits. This will probably tell you a lot more about whether it will work for you than comparing the specs of multiple models listed online. Check to make sure that you can fit your sleeping pad and sleeping bag inside, that the foot box is large enough for your feet.

More Winter FAQs

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About the author

Philip Werner has hiked and backpacked over 7500 miles in the United States and the UK and written over 2500 articles as the founder of SectionHiker.com, noted for its backpacking gear reviews and hiking FAQs. A devotee of New Hampshire and Maine hiking and backpacking, Philip is the 36th person to hike all 650 of the hiking trails in the White Mountain Guide, a distance of approximately 2500 miles, completing a second round in 2021. Philip is the author of Backpacking the White Mountain 4000 Footers, a free online guidebook of the best backpacking trips in the White Mountains in New Hampshire and Maine. He lives in New Hampshire.

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10 comments

  1. > That said, winter bivy sacks made with Gore-tex or Event are significantly more breathable (often by a factor of 2 or more) than bivy sacks made with the proprietary waterproof/breathable knock-offs like Black Diamond’s Nanoshield or the North Face’s Futurelight fabrics. They generally cost more, though.

    Really? Sorry, but that’s just plain brand-plugging & reiterating marketing bullsh*t.

    Without getting too technical, there are many kinds of Gore-tex, some more suitable for bivvy application than others. Worse is, you don’t know which kind you are getting, since it’s rarely mentioned in the advertising and Gore changes the names confusingly every few years (as do others).

    Such a broad statement is wrong. Decades ago, there used to be only two kinds of WPBs, PU hydrophilic (cheap knock-offs) and ePTFE microporous (Gore & eVent). Then Gore combined them up (most GTX uses both hydrophilic & microporous layers for protection of the membrane) and people liked eVent more for air permeability (at some expense of longevity). Then some Gore-tex types got air-permeable (used in a few bivvy bags to good success) and some got worse. Then came electro-spun PU membranes (Neoshell) that were more air permeable (better moisture management) than Gore-tex at the expense of longevity. Then came nano-spun PU membranes that could be tailored to anything you wanted (longevity, permeability & waterproofness – just not all three), making brand names meaningless.

    Please, do you research before you write something like that. Nowadays, the whole WPB field is so mixed up that without proper testing and specifics, such broad brand statements as yours are completely meaningless (e.g. the new Gore-tex Pro, not to be mixed up with old Pro, has three completely different fabrics with wildly different RET ratings, some of which would be completely unsuitable for a bivvy bag).

    • I think if you look at the different MVTR’s for these fabrics (if you buy into the fact that lab results mean anything in the real world), they actually are better than the stuff that’s not OEM’ed. But as you say, there are so many flavors and formulations of Goretex and Event, it’s hard to tell what any given waterproof breathable is or is supposed to do.

  2. Have you done a 3-season Bivy Sack Review? I could not find one.

  3. any ideas for stomach sleepers and restless sleepers on using a bivy bag and a winter sleeping bag….seems easy to end up facing into the insulation and breathing all that moisture into the bag overnight?

    • just the obvious. Use a different shelter, suspend the netting/top up off your face, or sleep with the top open. Same strategies you’d employ in a tent that suffers from heavy condensation.

  4. Hello there,
    Thank you for the information.
    I am preparing for sleeping in mountains with bivy (exped bvybag 100% ventair) (i practice in the garden at minus 10*C). it is perfect, but i would like to replace the maleable wire of aluminium by a flexible pole (3 pieces) to make more voluminous the headroom. Any idea where i can find this element?
    Thank you by advance, stay safe,
    David

  5. Hello , what can you say about millet bivy sack i want some durable materials but i am not sure about breathability about this bag.

  6. Any extra long for someone 6’7″ tall?

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