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.
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. )
|Model||Style||Weight||WTB Top Fabric||MSRP|
|Big Agnes Three Wire Bivy||Bivy Shelter||25||3 Layer Membrane||329.95|
|Black Diamond Spotlight Bivy||Bivy Shelter||18||Nanoshield||220|
|Black Diamond Twilight Bivy||Bivy Sack||10.7||Nanoshield||150|
|Black Diamond Big Wall Hooped Bivy||Bivy Sack||29||ToddTex||240|
|Black Diamond Bipod Bivy||Bivy Shelter||27||ToddTex||290|
|MSR E-Bivy||Bivy Sack||9||Silnylon||100|
|MSR AC Bivy||Bivy Sack||16||WTB||200|
|NEMO Gogo Elite||Bivy Shelter||19||OSMO||430|
|Outdoor Research Molecule Bivy||Bivy Sack||21.5||Proprietary||119|
|Outdoor Research Alpine Bivy||Bivy Shelter||32||Gore-Tex||245|
|Outdoor Research Advanced Bivy Sack||Bivy Shelter||39||Gore-Tex||320|
|Outdoor Research Aurora Bivy||Bivy Sack||24||Gore-Tex||200|
|Outdoor Research Helium Bivy||Bivy Shelter||18||Pertex Shield+||169|
|Rab Storm Bivy||Bivy sack||16.4||Hyperlite Storm||165|
|Rab Ridge Raider||Bivy Shelter||36.4||Event||375|
|Rab Ascent Bivi||Bivy Sack||22||Event||280|
|Rab Alpine Bivi||Bivy Sack||16.6||Event||265|
|Rab Survival Zone Lite Bivi||Bivy Sack||8.4||Pertex Endurance||150|
|Rab Survival Zone Bivi||Bivy Sack||15.5||Hyperlite Storm||120|
|Terra Nova Moonlite Bivi||Bivy Sack||6.7||Proprietary||149|
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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