Home / For Beginners / A Beginner’s Guide to Waterproof Bivy Sacks: How to Choose

A Beginner’s Guide to Waterproof Bivy Sacks: How to Choose


waterproof-breathable-bivy-sack
Bivy sacks were first developed as solo shelters for mountaineering and climbing where participants were interested in light weight and highly compressible gear. The original bivies were little more than waterproof sleeping bag covers that protected hikers and climbers from rain and snow or acted as temporary emergency shelters.

The Outdoor Research Alpine Bivy 'Shelter' incorporates a hooped pole that increases interior space and livability.
The Outdoor Research Alpine Bivy ‘Shelter’ incorporates a hooped pole that increases interior space and livability.

Since then, bivy sacks have evolved to include waterproof breathable fabrics and bug netting to help reduce internal condensation and make them more livable in warmer weather when increased ventilation is desirable. In some cases, hooped tent poles have been added to bivy sacks to create bivy shelters, making them more livable in stormy or inclement conditions when you need to stay in them for a longer period of time. (Non-waterproof bivy sacks also exist, but they really are just sleeping bag covers and can’t be used as standalone shelters in wet or adverse conditions. )

ModelStyleWeightWTB Top FabricMSRP
Big Agnes Three Wire BivyBivy Shelter253 Layer Membrane329.95
Black Diamond Spotlight BivyBivy Shelter18Nanoshield220
Black Diamond Twilight BivyBivy Sack10.7Nanoshield150
Black Diamond Big Wall Hooped BivyBivy Sack29ToddTex240
Black Diamond Bipod BivyBivy Shelter27ToddTex290
Borah Snowyside eVent BivyBivy Sack13.9Event160
Brooks Range Alpini BivyBivy Sack16Proprietary250
Exped 100% EventBivy Sack22Event369
Exped Event/PUBivy Sack22Event259
Mammut Sphere BivyBivy Sack10.9Proprietary100
Mountain Hardwear Dry.Q Bivy SackBivy Sack11.3Dry.Q189
Millet Bivy BagBivy Sack16DryEdge110
MSR E-BivyBivy Sack9Silnylon100
MSR AC BivyBivy Sack16WTB200
MLD Event Soul BivyBivy Sack13.5Event345
NEMO Gogo LEBivy Shelter34OSMO350
NEMO Gogo EliteBivy Shelter19OSMO430
Outdoor Research Molecule BivyBivy Sack21.5Proprietary119
Outdoor Research Alpine BivyBivy Shelter32Gore-Tex245
Outdoor Research Advanced Bivy SackBivy Shelter39Gore-Tex320
Outdoor Research Aurora BivyBivy Sack24Gore-Tex200
Outdoor Research Helium BivyBivy Shelter18Pertex Shield+169
Rab Storm BivyBivy sack16.4Hyperlite Storm165
Rab Ridge RaiderBivy Shelter36.4Event375
Rab Ascent BiviBivy Sack22Event280
Rab Alpine BiviBivy Sack16.6Event265
Rab Survival Zone Lite BiviBivy Sack8.4Pertex Endurance150
Rab Survival Zone BiviBivy Sack15.5Hyperlite Storm120
Sierra Designs Backcountry BivyBivy Sack12.7Proprietary130
Terra Nova Jupiter BiviBivy Shelter30Gore-tex410
Terra Nova Survival BiviBivy Sack12Proprietary74
Terra Nova Discovery BiviBivy Sack15Gore-tex390
Terra Nova Moonlite BiviBivy Sack6.7Proprietary149
The North Face Assault BivyBivy Sack15DryWall100
Titanium Goat Ptarmigan BivyBivy Sack6.4Intrepid90

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 lay out your bivy sack, slip your sleeping pad inside, and stuff your sleeping bag on top of your pad. There are no guylines to set up or tent stakes to pound into the ground, making it ideal for sleeping out in the open on rock ledges or in dense forest. Being waterproof, you don’t have to lie on top of a ground sheet either, since the bottom of a waterproof bivy sack is designed to keep you dry.

But two of the biggest advantages of waterproof bivy sacks are their light weight 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 add a few degrees of insulation to your sleep system, usually 5-10 degrees, which can also help reduce the amount of gear you need to carry.

Disadvantages of Bivy Sacks

Bivy sacks are much more confining then 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. Getting out and back in can also be challenging in rain, since you won’t have enough space to put on or take off rain gear when you need to get up to go to the bathroom at night.

Bivy sacks are also more prone to internal condensation than 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. In very humid and tropical environments, you’ll probably be better off using a tent than relying on the breathability or ventilation of a bivy sack.

How to Choose

When choosing a bivy sack or bivy shelter, make sure that get one that is completely waterproof with pre-taped seams if you plan on using it as a standalone shelter in rain, snow, or in a snow cave. Having a waterproof breathable top is also important to vent water vapor and help minimize internal condensation that can make your sleeping bag wet, but don’t overlook the need for vents or zippers which can be even more effective in reducing internal humidity.

Next consider what your priorities are. If you plan to camp in warm weather, make sure to get a bivy sack with a mesh panel over the face so you can sleep without insects biting your face at night. If you plan to sleep in a bivy sack in winter or in snow caves, a mesh panel will be less important. If hood room is important to you, consider getting a bivy shelter with an interior pole.

Check to see what ventilation options are provided, including side zippers so you can pull open the bivy sack completely if you are to warm. Check the shape of the foot box if you have big feet and the shoulder girth if you have big shoulders or prefer a wider space to sleep in.

Don’t forget to consider the weight of the bivy sack and its compressed size, since one of the chief benefits of using a bivy sack is gear weight and size reduction.

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.

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19 comments

  1. I’m surprised you don’t have the Katabatic Bristlecone, Zpacks Splash Bivy, or any of the Mountain Laurel Designs bivies listed, or are none of those waterproof? It may be worth expanding on your non-waterproof bivy sack comment. Also, isn’t small tarp + bivy sack a common strategy?

    Thanks again for the round-up of bivies and the detailed information.

    • They’re not waterproof – at least in the case of the Zpacks splash and MLD Superlight. They both have screens over the face and no way to close the front in the rain, snow, or wind. They’re intended to be used with a tarp overhead and not as standalone shelters. They’d be better classified as sleeping bag covers.

      • Thanks. Somehow I missed the MLD Soul Event Bivy in your list the first time through also.

        Unrelated question – any special considerations in snow storms – breathability, support? I imagine Gore-Tex won’t breathe too well with snow on top, but haven’t tried it myself. I could imagine being trapped under a good snowstorm.

      • If you anticipate heavy snow, get a bivy shelter – one with more structure. Or bring a shovel and build yourself a snow structure to provide yourself with ore protection. I suggest this book – “How to built and igloo and other snow shelters.” It’s really excellent. http://amzn.to/2geqF9W

  2. I backpack the Southern California Coast, mostly Los Padres and Big Sur. Rain is hardly ever a concern, so I use my old Mountain Hardware Conduit SL with by 45 degree down sleeping bag, mainly for added warmth and just in case some unforeseen rain occurs (had a few light sprinkles in the past). Recently bought a Marmot 20 degree bag and when it arrived found out it was made with “Down Defender”, Marmot’s water resistant down. Should I leave the bivy home next time and just “Cowboy” camp with this bag if no rain is forecast (I’m a wimp and would cancel or move trip if rain was forecast) for my 2-3 day trips?

    • “waterproof” (note quotes) won’t keep you warm when it gets wet (it’s just a sodden mess), although it will dry slightly faster. Bring the bivy. You don’t have to use it, but it will keep the cover of your sleeping bag drier if there’s a heavy dew.

  3. Thanks for this piece. I have no experience with bivy sacks. In the warm months, I use an MLD tarp and inner nest. I’m thinking that a bivy-and-tarp system would be a good way to go in the shoulder seasons, when you can have cold and rain at night.

    • If you have an inner nest, which is mesh plus a bathtub floor, there’s no reason to add a bivy sack in shoulder (cooler) season weather. I’d find that a LOT more comfortable and drier (no risk of condensation in the bivy sack) than sleeping in a bivy sack like the ones described here, which are designed as standalone shelters by themselves. The tarp/sleeping bag cover bivy style is really for use in warmer weather when you want something lighter weight than an inner tent (and you’re using a tarp shelter that is flat (squared cornered) rather than shaped), so it has a much smaller footprint.

  4. Nice article. Thanks for the links to many sacks!

    One thing you don’t mention that is nice to keep in mind is that it is much better if the zipper on the bivvy opens on the same side as the zipper on your sleeping bag. This makes access much easier. If the bivvy and the sleeping bag have opposite side zippers, it is a pain in the butt to get out to go pee at 3am.

    Yes,I speak from experience!

  5. When I was first starting out I got tired of lugging around my tent, so I found a good used OR Bivy on Craigslist.
    I used it on two or three trips in the early spring and I absolutely hated it. Being confined wasn’t the issue, as much as the condensation even with the top open.

    Still, I’m happy I have it. I bring it on all my winter hikes. I would also do long sections on the AT / LT with it. I planned to sleep in shelters, but brought it in case the shelters were full.
    Personally, I don’t recommend sleeping in a Bivy, but I think it’s a valuable piece of equipment for mountaineering and winter hiking.

  6. Ronald Turnbull’s The Book of the Bivvy gives a warts and all view and it is well worth a read. Personally I gave up using an eVent bivy after finding it coated my 0F sleeping bag with a layer of ice on a multi-day winter trip.

  7. I’m intrigued by your comment that a water “resistant” sleeping bag cover is really only useful with a small flat tarp.
    A blog post on when the tarp+bivy combo is best, and when a shaped tarp is best, and when a bug netted tarp tent is best – for people who like to pack small and light – but are on the east coast would be very useful :)

  8. Can you recommend one for last resort/emergency winter hikes in the Whites?

    • I’d go with the Rab Alpine Bivi. Rab bought Integral Designs a few years ago and they made excellent mountaineering bivy sacks out of Event. A lot of Rabs bivies are based on the old ID designs, which rocked.

  9. I solved the problem “where to put my personal stuff and the rest of my gear” by taking a silnylon duffle bag with me. Everything fits inside, including my backpack. Waterproof and organized, lightweight.

  10. I’ve got an old Inegral Designs bivi bag called the Chrysalis (I think). Has a waterproof, breathable top and waterproof base. Top half unzips and has a full-face bug net which can be sealed. Good kit. Can be totally weatherproofed and warm without a tarp. As you say, a pain to get in and out of in the rain.

    Under a tarp a MLD superlight bivi does the trick.

    I enjoy using my Vaude Bivi 1p though. Hooped bivi so not so claustrophobic.

  11. I had looked at bivy sacks and decided to go with an Alpine Hammock. Combination bivy sack and hammock. Being in New England, I haven’t used it on the ground yet (plenty of trees and too many rocks) but I like that it is a dual use item. Condensation isn’t too bad with the vents, only drawback is that it’s heavy for a hammock since it uses heavier material so that it can stand up to ground use.

  12. Joseph Buettner aka Nitrojoe

    I returned my Splash Bivy when I completed my thru hike of the CT this year. I had serious issues with condensation in the head and foot areas. My quilt sleeping bag would be soaked in those areas. I sent an e-mail to Zpack and they graciously said they would refund or exchange it. I asked what the problem might be for I have other bivys that don’t do that and they said it was a mistake to put a non breathable material in the head and foot areas and that they were going to redesign this item in the future. I liked this bivy for its light weight and ease of getting in and out of it also ideal for my floorless Solo Mid.

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