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Our testers used the bivy sacks in this review over all sorts of terrain - hanging off the sides of cliffs, basking in mountain meadows, and in riverside campsites in the desert. We waited out surprise storms at high camps and took them along on climbing, camping, bikepacking, and ultralight backpacking missions. With our field tests complemented by objective comparisons, we rate each product using key metrics. If you're looking for a great deal when it comes to weather protection, we've got the best choices for you to consider.
Waterproof and breathable material, supple fabric, plenty of room in toe box and around shoulders
Lightweight, breathable, packs down small
Comfortable, breathable and supple fabric, good weather-resistance
Lightweight, warm in an emergency, zippered opening, cinch strap to trap heat, more durable than most emergency bivy sacks
Extremely lightweight, very small packable size, good at reflecting heat
Cons
Too tight around hips, expensive, no way to suspend above your face, zipper too low and easily catches on material
Limited to colder and drier climates, tight fit around feet and torso
Heavy, zipper catches, hood wire is finicky
Tight fit for taller people, way too tight with sleeping pad and bag inside, water-resistant but not waterproof
Tears easily, no zipper or cinch strap closure, too short, non-breathable material
Bottom Line
While we loved the soft waterproof/breathable material of the Rab Alpine, the zipper catches frequently and the hood design doesn't allow you to suspend the material above your face
Ideal for light and fast missions in drier and/or colder climates
Breathable and resistant to weather, but heavier than its competitors with similar features
This emergency bivy sack works best in cold, dry weather and can be used on multiple outings as a weather-resistant shelter
This lightweight and very packable emergency bivy sack could be used more than once but might tear easily and has no way to tighten the opening to keep warm air trapped inside
The Outdoor Research Helium Bivy offers fantastic weather protection, comfort, ventilation, and breathability, all in a relatively lightweight package. Other models might offer high performance in just one or two areas — like the MSR Pro Bivy in packed size and weight — but the Helium is a true all-arounder. It performed way above average in most of our test metrics, and its overall score was higher than any other bivy sack during our testing process. Not only is it loaded with features, but the entire package comes in at about a single pound, pole included. Put simply, it combines everything we want in a bivy better than any other model we've tested.
We are thoroughly impressed with this bivy, so we'll do our best to be objective and point out its weaknesses. With that in mind, know that if you're looking for the burliest, most durable model, the OR Helium isn't it. This model is intentionally designed to be a lighter-duty version of the heavier-duty, more protective alpine bivy sacks. So, direct your attention towards the Outdoor Research Alpine AscentShell if you need a burlier option with optimum weather resistance. In a perfect world, you would have a different and specialized bivy for every situation. In the real world, you're probably limited to one, and the OR Helium bivy performed excellently in every test we threw at it, from heavy rain to not weighing down our pack for extended outings.
We were originally attracted by the Helium's claimed weight, but this bivy surpassed our expectations and has become one of our all-time favorites.
The Katabatic Gear Piñon Bivy astonished us with its lightweight, roomy, and therefore breathable interior and an extra-large mesh opening that made getting in and out a breeze. Designed for the lightweight aficionado, this bivy is intended to be used with a lightweight tarp and some paracord to deflect precipitation. While it wouldn't fare well in a downpour with high winds like the Outdoor Research Alpine AscentShell, we would gladly bring it into the backcountry with a reasonably good weather forecast.
The Piñon Bivy lives up to its name, perfect for montane ecosystems where you can string a cord between two trees and attach another short piece of cord to a loop at the top of the bug netting, perfectly suspending the mesh. Rigged correctly, there is plenty of breathing room above your face and plenty of air flow for you to get a good night's rest in the woods. With an inexpensive cost, you won't be disappointed with the Piñon Bivy if it matches your style of backcountry travel. On the other hand, if you require better protection in rainy conditions, the Outdoor Research Helium Bivy is a prime pick that also won't cost you top dollar like other premium models.
With a tarp strung between two trees and a cord suspending the mesh upper, the Katabatic Gear Pinon Bivy makes for an excellent home in the outdoors!
Probably not long enough if you're over six feet tall
Expensive
SPECIFICATIONS
Packed Size
3.5" x 12.25"
Measured Weight
19.9 oz
Waterproof?
Yes
Open Length
83"
Shoulder Width
28"
The Outdoor Research Alpine AscentShell is an extremely weather-resistant bivy sack designed to deflect all of nature's elements in the alpine environment. It performed really well during our testing, scoring highly in all of our metrics, though others (like the 7.6-ounce Katabatic Gear Piñon Bivy) were lighter weight. The Alpine AscentShell is just under 20 ounces, only a bit heavier than many of our top-scoring models. We were very impressed with how packable this bivy is, especially considering its burly construction and high performance, resisting rain, wind, and snow. The side zipper has smooth action and allows ease of entry and exit while ventilating moisture.
While OR Alpine AscentShell offers excellent protection from the elements, the tightly woven fabric isn't very breathable in favorable conditions. Taller individuals might find the length is a bit too short. As one of the pricier contenders we tested, one must consider whether the high-quality construction is worth the high cost. If you are not ready to invest, the Sierra Designs Backcountry Bivy is a breathable option at a fraction of the price. Regardless, the AscentShell is our top recommendation for inclement weather.
Cozy and warm on a cold and clear winter day, the OR Alpine AscentShell bivy protects you from the elements while letting you enjoy your surroundings.
The MSR Pro Bivy comes out on top in the weight-to-protection ratio. Weighing in at an impressive 9.1 ounces, the MSR Pro is a fantastic solution for those looking to add an insurance policy to their exposed ridge scramble or ultralight overnight. On the surface, this bivy appears to be something to reserve just for the unexpected emergent rain shower. Still, depending on your tolerance for discomfort, this could serve as an extremely lightweight shelter for longer excursions.
The Pro Bivy is more of a specialized tool rather than an all-arounder. If you need a bivy that can withstand a big storm, check out the Outdoor Research Helium. If you're in the market for a bivy strictly for emergencies, the SOL Escape Bivy is our favorite. However, as an emergency shelter or for ultralight missions into the hills, we think the waterproof fabric, ample footprint, and ease of setup make this model a welcome companion.
This bivy is best suited for emergency situations or as a backup.
The SOL Escape Bivy is a remarkable and simple emergency bivy. We have used ours on and off for over a year, and it has held up well, which is asking a lot from an inexpensive emergency bivy. In our most recent testing phase, a small tear occurred, so we contacted SOL, and they immediately offered to replace it for free. If you're on a budget and want to ensure you have a little extra warmth and protection in your pack, the SOL Escape is a good choice. The proprietary “metalized spun-bonded olefin” fabric proved to be lightweight, very weather-resistant, breathable, and added a significant amount of warmth to the 35-degree sleeping bag that we used during testing.
If you're venturing into a cold and dry climate, you could certainly get by with the SOL Escape as your primary shelter. However, the footprint is far too small unless you're under 5'11" and 175 pounds, and this model can't be fully closed. While the SOL Escape is certainly a far cry from premium bivy sacks, like the Outdoor Research Helium, it is an excellent emergency shelter you can use over and over without losing the attributes that make it so functional.
It's hard to leave the relative comfort of the Escape on frosty mornings.
Credit: Brian Martin
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We have tested bivies from the mountains to the desert to the coast.
Credit: Brian Smith
How We Test Bivy Sacks
We considered over 40 different models during our research process before buying the top 10 contenders to put to the test for this review. We examined how well they protected us from wind and precipitation and how they vented and transferred moisture from inside to out. We also paid attention to packed size, weight, comfort, and compatibility with other items. Testing was conducted in the field in various environments, from swampy conditions to snow to rocky ledges. This review is the distilled knowledge we gained from multiple seasons of intensive testing, and we hope it will serve you well in your own selection process. See our full How We Test article to learn more about our test regimen.
Our bivy sack testing is divided across five different metrics:
Weather Resistance (25% of total score weighting)
Weight (25% weighting)
Comfort (20% weighting)
Ventilation (15% weighting)
Packed Size (15% weighting)
Why Trust GearLab
This review is brought to you by OutdoorGearLab Review Editors and multi-discipline outdoor athletes Brian Martin and Brian Smith. As a former member of Yosemite Search and Rescue, Brian Martin was tasked with researching, testing, and replacing team equipment. This, in addition to his lifestyle centered around various outdoor pursuits, gives him a keen understanding of the features to look for in all kinds of outdoor equipment. He's as familiar with rock climbing as he is with backpacking or mountain biking, and he brings this broad experience to help readers discern the advantages and disadvantages of different products for different pursuits. Brian Smith is a certified IFMGA/AMGA American Mountain Guide based in Jackson Hole, Wyoming, and spends multiple nights per year camped out in the snow, in the desert, or at a bivy site on the side of a mountain. Whether guiding skiing, rock climbing, ice climbing, or alpine climbing, Brian uses outdoor gear more frequently than most human beings on the planet. His keen eye for detail lets him catch mistakes before they happen in the mountains as well as recognize high-quality gear that facilitates having memorable experiences in the outdoors.
Swampy campsites are ideal for a bug net bivy sack.
If pitching in a storm consider finding additional shelter, like a rock-cave below a pair of boulders.
Analysis and Test Results
Whether or not to bring a bivy depends on many factors, and everything from weight to the weather forecast to the available space in your pack can influence the decision. Before purchasing a bivy sack, consider the conditions in which you will use it. The high mountains in winter? A boggy swamp in spring? Each of our reviewed products has unique characteristics that might create a compelling reason to consider it for your next outing.
What's the Best Value?
We aim to bring you the best of the best, but also the highest value, especially when it comes to performance and cost. Our team of experts put each model through a series of tests, awarding scores for a series of metrics. Determining which bivy will suit your needs will certainly involve a list of pros and cons. What are you looking for? If the best value tops your chart, look for the highest-performing product from our scores that fits your price range. Standing out among the rest for value, the Katabatic Gear Piñon Bivy is hard to beat with its low cost, lightweight and packable size, comfort, and breathability (but requires a tarp and some cord to improve its water resistance). The Sierra Designs Backcountry Bivy covers what most folks need from such a product (low weight, comfortable, and weather-resistant) without costing as much as most premium models. Or for emergency protection on a budget, the SOL Escape Bivy offers the extra protection and warmth you might need when the unexpected occurs but also doesn't put you out a ton of cash. As always, we recommend finding the product that fits your performance needs and financial limitations.
Waking up warm and dry on an exposed bivy ledge in Zion National Park.
Credit: Joe Stern
Weather Resistance
From emergency bivys to the ultra-protective alpine expedition models, it's important to have a firm understanding of the characteristics of the bivy you're considering. Does it make sense to have an ultralight emergency bivy as well as an alpine heavyweight? Whatever your needs are, we thoroughly tested each of these bivy sacks within their intended boundaries (and beyond) to know where their limits really are. Waterproof fabrics and the ability to fully zip and enclose the sacks are a couple of key performance considerations.
The most weather-resistant bivy sacks we tested were the Outdoor Research Alpine AscentShell and Outdoor Research Helium. Both were fantastically waterproof and offered substantial protection from the elements. In our opinion, these models provide the best balance of durability, warmth, and overall protection.
Different types of fabrics work best in different situations. A fully waterproof material, like Gore-Tex, will keep all the rain out, but even the most breathable fabrics have a hard time letting water vapor from sweat and breathing escape. Ripstop nylon is lightweight and waterproof, if treated with a durable water-repellent (DWR) coating. It's typically more breathable, but it's only ideal for a light rain since it isn't entirely waterproof. The SOL Escape deviated from the norm by constructing a bivy from metalized spun-bonded olefin, which is typically used as a moisture barrier for home construction. This material provided excellent weather resistance while maintaining some breathability. However, because this option doesn't close all the way, its protection from the elements is minimal.
10-year-old Stella was gracious enough to help us test bivy sacks in the shower and gave us a thumbs up on the OR Alpine AscentShell.
Credit: Brian Smith
Some bivy sacks are made for four-season protection and can be used in wintry, alpine conditions. Other models strive to save weight and don't allow for a complete closure of the waterproof shell material around the face, so they're best reserved for emergencies or milder rain and temps. The least protective are also often the lightest options. Just because they can't keep you warm and dry in a heavy downpour doesn't mean they don't have their place. These lightweight emergency bivys can be worth their weight in gold for fast and light ascents, long trail runs, or fastpacking when some extra protection is warranted.
Weather resistance should be high on your list of considerations if you plan to camp in the winter months.
Credit: Brian Smith
Like all camping shelters, the way they're used can affect weather resistance. When possible, selecting higher ground or a clearing under a tree will add a bit of extra weather protection and avoid pooling water in a nasty deluge. Always check the trees overhead for dead limbs or “widow-makers,” which can break off dangerously (especially in a storm).
Weight
When hunting for a bivy sack, it's important to take a mindful moment to imagine what exactly you're going to be using it for. Before you look at weights and packed size, make sure the bivy will perform at the level you need it to. If you're venturing into a snowy alpine environment with likely precipitation, you want something you can comfortably spend a lot of time in and that you are confident will keep you dry. If you're heading out on a burly all-day ridge climb but aren't sure if you will have to bivouac, a lightweight emergency option might be more appropriate.
If you're just getting into the ultralight game, there are some fantastic options on the market that offer decent protection against those surprise rain showers or windy nights. The lightest reusable bivy we tested is the SOL Escape. Most bivy sacks weigh less than two pounds and are far lighter than the best backpacking tents. Our top recommendation overall, the OR Helium, weighs just over a pound. If you are willing to add a little weight to increase weather resistance, the OR Alpine AscentShell is roughly 20 ounces, which is much lighter than several models that fell short in our inclement weather tests. Keep in mind, though, that there are some ultralight tents that contest some of the heavier bivy sacks, and they're much more spacious.
While the MSR Pro weighs a bit more than the SOL Escape, it offers a significant advantage in comfort and weather protection, which we think is well worth the few extra grams.
Credit: Brian Martin
Comfort
Comfort is always an important criterion for outdoor gear, especially for gear that you rely on for shelter in backcountry situations. Time spent in an uncomfortable or cramped bivy with creepy crawlies getting inside can turn a user away from bivy sacks for good. Contributing factors to each bivy's comfort rating include insect protection, roominess (volume and floor plan), ease of use, and added features, such as gear pockets or straps to hold your sleeping pad in place.
If you choose a bivy because you want a shelter that weighs less and takes up minimal space in your pack, you should expect less space for you inside — just hopefully not to the point of discomfort. We compared floor space, head space, and shoulder width when assessing our comfort ratings. The OR Helium and OR Alpine AscentShell earned the top scores for this section of our assessment. Both employ a singular pole that allows for extra breathing room and even enough space to read a book.
Having ample headroom during a downpour is one of the most critical points in maintaining some element of comfort in a bivy
Credit: Brian Smith
Ultralight and minimalist models can often be less spacious to cut down on the amount of material used. Conversely, four-season models often have wire hoops or tent poles to help increase volume, leave room for the face, and provide an experience very similar to sleeping under the stars with all the protection of a tent. The Sierra Designs Backcountry Bivy is an excellent combination of size and comfort features, such as the ability to keep the ceiling away from your face with no added weight. The SOL Escape is on the snug side but still usable for our 5'11" gear tester.
The extra space created through this simple system was enough for us to read a book and get comfortable during a rainstorm.
Credit: Brian Martin
Ventilation
Ventilation in bivy sacks can be a tricky thing. Like any piece of waterproof gear, typically, the better a sack protects you from rain and weather, the less it breathes. How well a bivy ventilates and how much condensation builds up inside is a huge factor in its versatility and performance.
Many human factors can make your night miserable even in an exceptional bivy, so here are a few actions you can employ to make sure your bivy will perform to its highest abilities. The main issue is that your condensed breath or extra sweat from getting overheated can build up inside the sack, causing a “rain” effect when moving or shifting inside. One of the easiest things to do to prevent condensation if you have dry weather is to keep the zippers open as much as possible. Even during downpours or extended periods where complete protection is necessary, we recommend “cracking” the mesh or zipper to allow some ventilation of the condensed air inside.
A clamshell opening and mesh bug screen allow for ample ventilation during a rainstorm or during nicer weather.
Credit: Brian Martin
If dry weather is not in the forecast, the two critical things to keep in mind are to make sure your breath is directed toward the outside of the sack and to use a sleeping bag and pajamas (or whatever clothing you sleep in, if any) that are the appropriate warmth for the temps. If the temps are variable, or you toss and turn in your sleep (and can't easily ensure your mouth stays at the bivy opening), it might be a good idea to bring a synthetic sleeping bag instead of a down sleeping bag. Why? Synthetic insulation will retain its insulating properties and keep you warm if it gets damp or even soaked.
As the entire top portion of the MSR bivy is open, we had no ventilation issues. If you pack along some para-cord, you can elevate the front flap over your head, creating a little extra space.
Credit: Brian Martin
If your bivy can be staked out or has a pole to give you space around the head, taking advantage of these features will add extra air space between your body and the bivy walls, which significantly improves its ability to ventilate. The Outdoor Research Helium and the Outdoor Research Alpine AscentShell both have this feature, making them more comfortable than models that let the fabric rest against your face.
The slight difference of having the bug net/ventilation elevated above your face did two things. It paid huge dividends for comfort, and helped the bivy vent more efficiently.
Packed Size
No matter what you intend to do with your bivy, packed size is important. Space in our haul bags, backpacks, and bike bags is always at a premium. Having a bivy that is lightweight and can be crammed into a tiny package is essential. By dropping down from a tent to a smaller bivy, you should be able to save several liters of space, allowing for a smaller pack overall or room for other essential gear. Taking this even further, if you opt for an ultralight bivy, you might even be able to pack it down to the size of a soda can, saving loads of space in your pack.
We measured each product when packed up in its (usually provided) stuff sack. Some models have poles that could be added to the same stuff sack or stored in your pack separately. The Survival Frog Tact Bivvy 2.0 offers the smallest packed size of all the products tested (2" x 4.5"), but it's more of a single-use bivy because it can be easily torn and rendered useless (think giant yard leaf bag). A much more durable and highly affordable model, the Sierra Designs Backcountry Bivy, measures 3" x 9.5". Lastly, the top-tier high-high performance OR Helium and OR Alpine AscentShell measure 4" x 12.5" and 3.5" x 12.25", respectively.
The TACT is for those wanting to go fast and light and reserve crawling into the bivy for emergency situations.
Credit: Brian Martin
Conclusion
Climbers, mountaineers, and ultralight backpackers alike may be interested in a bivy sack for numerous reasons. In addition to being a lightweight emergency shelter, these products can be a lower-weight and smaller alternative to a tent. A bivy's smaller footprint can also allow you to sleep in a multitude of places where a traditional tent would not be possible. Many factors need to be considered when selecting a bivy, ranging from weather resistance to pack size.
