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.
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
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
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
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.
Summary
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.
For ultralight adventures, I recommend the MSR Pro Bivy. For an emergency bivy you can carry on every trip, I recommend the SOL Emergency Bivvy.
