While no one wants to spend an unexpected night in the backcountry, it’s much better to plan for the possibility than to be caught off guard. I carry a small bivy sack on most mountaineering trips to ensure that I always have shelter in case of an emergency.
A bivy sack can also be a great option for overnight climbing trips where you want to travel as fast and light as possible. You probably won’t sleep as well in a bivy sack as you would in a tent, but opting for an ultralight shelter can save you a pound or more of weight.
In this guide, I’ll review the 7 best bivy sacks for emergency use and ultralight climbing trips and explain how to choose the right shelter for your next trip.
My Review Process
I’ve spent years climbing, skiing, and mountaineering, and I carry a bivy sack with me on the vast majority of trips. It’s a critical piece of my emergency kit as well as my shelter of choice on light and fast overnight climbs.
I’ve slept in a number of bivy sacks over the years and know what separates the best shelters from the rest. For me, weight is a major priority when choosing a bivy sack. I want my shelter to be as light as possible while still providing protection from the elements. I also look for waterproofing and ventilation, since staying dry is critical to staying warm on cold nights in the mountains.
My favorite bivy sack to use is the OR Helium Bivy. At 16.3oz, it’s not the lightest bivy on the market. But for a few added ounces compared to competitors, I think it’s the most comfortable, the most weatherproof, and the most breathable.
The Helium Bivy is made with a Pertex shell that does an excellent job shedding water while allowing condensation out of the bag. It’s surprisingly spacious on the inside and I’ve found that there’s more than enough headroom to sleep in comfort.
There are few drawbacks to the Helium Bivy. The price is fair and it’s well-designed for those who want to go light, but prefer comfort over going ultralight.
The MSR Pro Bivy is unbelievably lightweight at only 8.9 ounces. That’s just more than half the weight of the Outdoor Research Helium Bivy. If your goal is to go as light as possible, it’s hard to beat the Pro Bivy.
Of course, you give up some waterproofing and comfort along with that extra weight. The closure is just a flap of material, with no zipper. So a strong wind can easily blow rain into your bivy. There’s also no pole to keep the bivy sack off your face, so don’t expect to sleep particularly well.
Overall, I’d recommend the Pro Bivy as a crossover between a tent replacement and an emergency bivy. It’s best for trips where you need to go as light as possible. But for trips where you can afford a few extra ounces, I’d opt for a more comfortable bivy sack.
The Sierra Designs Backcountry Bivy offers a great value at a relatively affordable price point. This bivy weighs in at just 13.6 ounces and packs in a ton of comfort features to boot.
My favorite thing about the Backcountry Bivy is that it features a full-length zipper. If you’re using this bivy in lieu of a tent, this makes it much easier to ventilate when it’s dry outside. There’s also a bug bivy net, which can be a big advantage during summer trips.
The Backcountry Bivy doesn’t have a pole, but rather an attachment point that you can tie off to suspend the bag away from your face. This works great if you have a tree handy, but the design doesn’t always work in your favor in the alpine.
The Black Diamond Bipod Bivy is effectively a cross between a tent and a bivy sack. The large pole creates plenty of headroom, although it’s important to note you need to stake out the bivy to take advantage of all the extra space.
What really sets this bivy apart is the heavy-duty construction. It’s about as waterproof as a 4-season tent and locks in more heat than most lightweight bivy sacks. Breathability suffers a little bit, but condensation build-up inside the sack is manageable.
At 28 oz, it’s worth thinking carefully about whether you simply want to carry a tent. But for bivvying in winter weather, the Bipod Bivy is a good option.
The Rab Alpine Bivi is about as simple as a bivy sack can be. There’s no pole, no bug netting, and only velcro tabs for creating ventilation holes.
The simple design can be an advantage if it’s stormy out and you want to jump in your bivy sack as quickly as possible. But it also means that you’ll be sleeping with the bivy sack up against your face.
The Alpine Bivy does an excellent job moving moisture out of the sack. It also has a waterproof floor, making it a good option for stormy nights.
The SOL Emergency Bivvy is the emergency bivy sack I carry with me on almost every day trip. It’s cheap, extremely lightweight, and packs down small. The material is also surprisingly durable, which means this isn’t a one-time-use bivy sack.
Thankfully, I haven’t had to test this emergency bivy in any extreme conditions. But I’ve found that it retains heat well and doesn’t generate an excessive amount of condensation over the course of a single night in dry conditions. If it’s raining hard, you’ll have to hold the top of the sack closed to keep water out.
The SOL Escape Bivvy is a heavier-duty version of the Emergency Bivvy. It’s a few ounces heavier, but offers more durable material, better body heat retention, slightly better weatherproofing.
The bivy has a basic drawstring closure system, which is only modestly effective at keeping out heavy rain. It’s also worth noting that this bivy sack will just barely fit anyone who’s six feet tall.
I like the Escape Bivvy for ultra-long day trips where spending the night out seems reasonably possible, if not the plan. It’s fairly inexpensive and, while not comfortable, will keep you warm for a night if needed.
Bivy Sacks vs. Tents
You probably already have a tent, so you may be wondering why you need a bivy sack for hiking and mountaineering.
The first reason is that a bivy sack serves as an emergency shelter. If you’re out on a day trip and aren’t carrying a tent, you can bring a bivy sack along and add only a few ounces of pack weight. In the event you get caught out overnight—because your trip took longer than expected or because of an injury—the bivy sack will provide protection from the elements and help keep you warm.
I carry an ultralight emergency bivy sack on almost every day trip. If I’m carrying a tent, though, I don’t usually carry a bivy sack in addition.
The other reason to have a bivy sack is that it can be used in place of your tent on trips where you want to move as quickly as possible. Most of the bivy sacks I recommended weigh less than one pound, whereas the best tents for mountaineering can weigh four pounds or more. That’s a big difference in weight.
Personally, I’m willing to give up some comfort and save three pounds for many one-night trips into the mountains.
Emergency Bivy Sacks
In my experience, it’s worth carrying an emergency bivy sack on any hiking, climbing, or mountaineering trip when you don’t have another lightweight shelter. For a weight cost of just a few ounces, an emergency bivy provides a lot of insurance if your trip goes sideways.
A night out in bad weather could easily result in hypothermia. An emergency bivy won’t keep you completely toasty and dry, but it will keep you sheltered enough to survive until the morning. You’d be surprised at how effective an emergency bivy can be, especially if you have a good down jacket with you.
Even if you don’t plan to be out long, it’s worth keeping a bivy sack in your pack as a backup plan. You never know when a small injury like a sprained ankle could leave you stuck in the backcountry and in need of help.
Importantly, a personal locator beacon isn’t a replacement for a bivy. I believe every mountaineer should carry a beacon, but rescue isn’t guaranteed to be quick even if you can call for help. Bad weather conditions can delay rescuers for a full day or longer, and you need to be prepared to survive on your own until they can get to you.
How To Choose The Best Bivy Sack
There are a couple things to consider when choosing a bivy shelter.
Dedicated Shelter vs. Emergency Bivy
First, you’ll need to decide whether you plan to use your bivy sack as a dedicated shelter in lieu of a tent on some trips or whether you just want an emergency bivy.
If you’re looking for a shelter, comfort matters and it’s better to add a few ounces for features like ventilation. If you’re looking for an emergency bivy, opt for the lightest possible bivy that is fully weatherproof.
Ventilation is one of the most important aspects of any bivy sack. There’s nothing worse than waking up to find that the inside of your bivy is covered in condensation and that it’s starting to soak through your down sleeping bag.
A bivy sack’s ventilation mostly comes down to the materials it’s made out of. Waterproof, breathable materials like Gore-tex, Pertex, and eVent are best. In addition, some bivy sacks offer built-in vents and mesh panels so you can air out the bivy sack when it’s not raining.
Comfort in a bivy sack largely comes down to how spacious it is, particularly in the head area. The most comfortable bivy sacks have a single pole or similar structure to keep the sack off of your face. Minimalist bivvys sacrifice the pole, so you will likely end up sleeping (or, rather, not sleeping) with the sack stuck to your face.
Weight is a huge factor for me when I’m comparing bivy sacks. The heaviest bivy sacks weigh around one pound—much lighter than a tent, but hardly ultralight. Generally, the lighter a bivy sack is, the less comfortable it will be to sleep in and the fewer features it will offer.
The best bivy sack can allow you to take on fast and light adventures without a tent or provide shelter for an unplanned night out.
My top pick is the Outdoor Research Helium Bivy, which provides an outstanding and comfortable shelter while weighing just one pound.
*The information on this site is based on research and first-hand experience but should not be treated as medical advice. Before beginning any new activity, we recommend consulting with a physician, nutritionist or other relevant professional healthcare provider.