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

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
MSR E-BivyBivy Sack9Silnylon100
MSR AC BivyBivy Sack16WTB200
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
Terra Nova Moonlite BiviBivy Sack6.7Proprietary149

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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  1. I am a novice. I am wanting to get a sleeping set up for someone who doesn’t have a home. Tents are not an option. Do you put a sleeping bag inside of the bivy sack?

    • Yes, usually you lay a sleeping pad (air or foam)’ then you sleeping bag on top of the pad. All enclosed in the bivy. Think of it as a mini 1 person tent.

  2. Why no mention of the MSS? At first I thought because of the weight but there are a few on your list that weigh more

    • I have no idea what that is.

      • MSS is the military Modular Sleep System. Goretex bivys usually go for about $50 on Ebay in new or excellent condition. The troops LOVE them. Comes in several camo patterns.

      • That doesn’t mean their good for civilians. Every piece of “used” military surplus I’ve bought has smelled like something died in it and had to be thrown out.

      • Be that as it may…

        Right now, today, brand new Gore-Tex bivys that are still sealed in the orginal plastic bag are on Ebay at $59.99, delivered.

        The bivys are genuine Gore-tex and made in the USA by Tennier Industries of Tennessee.

    • Nice system, but way too heavy

  3. Kevin,

    That’s strange I have used an Alpine bivy for years and never had major condensation issues. The only time I have had some condensation is in Scotland when I got buried in snow. The secret is to make sure your face is near the opening so you don’t breath into the bivy sac. Biviys are good if you are really tied and because you can just roll them out an go to bed, on the other hand they are a pain in ass if you have to get in and out of them when its raining. It can also be a bit scary if you get bears sniffing around because there is no way of quickly exiting most bivy sacs.

    The whole tarp vs bivy vs tent vs hammock debate has changed a lot when you consider is how much lighter tents are now than even 10 years ago. A solo tent like the Six moons Trekker weighs less than an OR Apline bivy, much less if you use trekking poles and don’t need to pack the two poles that weigh 6 oz. I think the tent and stakes are 26oz vs the Alpine Bivy at 32 oz. They also do a cheaper version called the Scout, it weighs 34 oz but is an absolute bargin for at around $125. Unlike a bivy sac the Trekker is big enough to get your gear inside. Big Agnes also offer a number of sub 3lb tents, I went for the Six Moons because of they are longer so better if you are over 6ft.

    I still use the bivy in summer especially in the Sierras where the weather is usually good but man eating ants are a real problem.:-)

  4. What’s all this talk about getting up to pee at night? Just take a hospital jar and let’er rip. Dump it a.m. Sheeeesh!

    • some of us with lady bits don’t have that an option, espec not in confined spaces – easier to squat over a jar in a tent, harded in a bivi. shewees help a big but still don’t fancy taking the risk of splashing my sleeping bag!

  5. I got a little bit lost a couple of weekends ago on the Cumberland Plateau in Tennessee. The daylight was fading and I started to worry that I’d have to spend the night out in the woods. Even with a headlamp, walking at night is treacherous in this area. There was still snow on the ground, and the temperature was going down to 30 that evening. I had a SOL Emergency Bivvy, but wonder if it would have kept me warm enough. Now I am wanting to carry a better “emergency” bivvy when I hike in areas that aren’t well-marked or mapped. Any suggestions? I want something really lightweight and non-bulky if that is possible. I am not looking to replace my tent with a bivvy, I just want the best emergency option.

    • Unless you carry a sleeping bag and some sort of insulating pad, a bivy isn’t going to do you any good. Bivy sacks don’t insulate and you’ll probably go hypothermic if you try lying in your emergency SOL bivy on the ground. I carry insulated pants, puffy down jacket, and a stove on all of my winter solo hikes and if I’m alone, I often carry a foam pad and a sleeping bag.

  6. Hello
    I was wondering, I have an OR bivy advanced and hike with it extremely windy, cold and wet surroundings of Faroe islands and Iceland. When it rains the cover touches my sleeping bag, which makes it feel not wet, but moist. Is there a tip on how to improve that? I thought of covering my bag with my camping towel, but maybe there is something else?

    • It’s condensation. The only way to prevent it is to have more airflow and avoid having the two materials from touching one another…as in get a tent.

  7. I have a Feathered Friends bivy sack which is probably about 15 years old and no information about it as they obviously no longer are involved with the manufacture of bivy sacks. Wondering if you had ever seen or used one? I have it solely for an emergency type shelter.

  8. On the bivy question. I have several of the high dollar commercial units, including the so called breathable units. None of them work. All condense enough water to make my sleeping bag wet.

    I did buy one of the USMC gore tex units off ebay for around 50 bucks. It does not smell at all. It has much less condensation than the commercial units, still not totally dry but beats the commercial bivy bags by a ton.

    Wiggys has a new Ducksback bivy out that I may try next.

    • Condensation is often unavoidable without ventilation. That’s why a lot of the higher end OR bivy sacks have meshed in windows so you can increase airflow.

  9. I have played with bivies (1 lb goretex) and oversheets of plastic or tyvek. They are only good if it is not going to rain. So far, what works best if it is not going to rain is a 5 X 8 tarp at 6 oz. It does work if it is going to rain, but site is very important then. If it might rain, an 8 X 8 tarp makes sense if there is room, or a 1 man tent at 14 0z if wind too. All of the above makes sense if there are few/no bugs. If bugs, a Zpacks tent is worth the money. All these are lighter than most of the bivies in your article.

    • Most of these bivies are for winter use. You probably wouldn’t use a zpacks tent because it’s too well ventilated and cold.

  10. Are there bivys for fat people? 100% serious question. I’m 5’9″ 325lbs so I have concerns about fitting in one.

  11. Wondered if anyone has had experience using the OR molecule bivy with a small pole. I got a “deal” on the OR molecule and a separate small pole that I found at a local shop that was supposed to be compatible with the Molecule. Unfortunately not. I’d still be interested in rigging it with the pole though as it would improve ventilation.

    Pole interior just falls over and might risk puncture of the bivy. Pole on exterior might work if used with a peg and the built in loop. Ideas?

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