Why Use a Bivy Sack?
The original idea of a bivy, or bivouac sack was a light and small option that can provide an emergency shelter and warmth if necessary. Comfort has always been sacrificed by users of bivies for the sake of reduced weight and small packing size. Early bivies were simple waterproof sleeping bag covers that would keep the rain off but were plagued with condensation issues inside the bag. Modern bivys use lightweight materials that provide water protection while still remaining breathable to reduce condensation issues.
Today, bivy sacks are popular not just with climbers looking for emergency shelter in case they get stuck overnight, but also with ultralight backpackers and bikepackers as an alternative to a tent or ultralight tarp.
However, a bivy is not for everyone, and today they face strong competition from ultralight tents and tarps (see our Ultralight Tent Review for more info on the best ultralight tent and tarps). Zpacks Duplex is a two-person tent that actually weighs less than our Editors' Choice Outdoor Research Alpine Bivy, but the Zpacks Duplex provides two people a much more comfortable shelter and better weather and bug protection. An ultralight tarp is is another option, and a two-person tarp like the Hyperlite Mountain Gear Square Flat Tarp is lighter still (just 10.2 oz) and offers better rain protection than some bivys.
So, why use a bivy at all?
- Light — When compared to a traditional tent, bivies are almost universally lighter for the price and protection you get. Ultralight tents and tarps can offer solutions with similar or even less weight especially if you're in a group of two and can split the load.
- Small Packed Size — The small packed size allow you to take an even smaller backpack than you might normally take. Some individuals even leave their sleeping bag inside the bivy and pack it as such. This lets you deploy your sleeping system in only a few seconds.
- Simplicity — Setting up a bivy can take only a few seconds, whereas erecting a tarp or ultralight tent can take maybe ten minutes. Consider the amount of time it takes for cold fingers to stake out guy lines or get poles set up just right. The moment the sleeping bag is in the bivy, you're good to go.
- Warmer sleeping — A bivy can improve the effective temperature range of a sleeping bag by as much as 5F. Some ultralight hikers use this capability strategically, allowing them to use a lighter ultralight sleeping bag, and thus shave off a pound or more from their overall pack weight. Keep this in mind as a low weight solution to colder climates when you don't want to buy a bigger bulkier sleeping bag. The smaller options such as the SOL Escape bivy offer excellent warmth at the fraction of the weight and cost of a bigger sleeping bag.
- Four-season — Bivies can offer better winter performance than many competing ultralight tent solutions, and the Outdoor Research Alpine Bivy is well suited for four-season use.
- No room, poor comfort — A tent offers the ability to sit up and have your morning coffee with your stuff inside. Not so a bivy (with the exception of the Outdoor Research Alpine Bivy, you will likely need to keep your gear in the pack at night. In sustained weather, a tent is a much better place to wait out a storm. Check the weather before you go, if inclement weather is imminent, a tent or tarp with more coverage might be your best bet. That being said, if you're going light, and are armed with the Outdoor Research Alpine Bivy you might be able to cram everything inside. Do a "Dry" run before you go! No pun intended.
- Solo only — If you had two or more people, an ultralight tent will typically offer a better solution than two bivys when you add up the weight and size. That said, if you have multiple people and utilize a tarp, having emergency style bivies along can augment the tarp and offer extra warmth and protection in nasty storms.
- Not great in sustained rain — Some bivys have an opening for breathing at the top that is not fully covered (in fact, it needs to be a bit open to provide proper air). You can roll over and sleep on your stomach to prevent rain from coming in, or put a jacket over your head. Some ultralight enthusiasts use a tarp in combination, which can provide a much better solution in the rain than a bivy alone.
- Bug protection — Only two of the bivies in this review offer bug netting, and none offer a comfortable place to hang out protected from the bugs. Again, if you're traveling through an extremely buggy environment, consider bringing along a tent, or ultralight tarp with a bug net. These options will keep you happy and offer a bedbug-free night.
- Condensation — It is nearly impossible to avoid condensation buildup inside the bivy sacks. While the tyvek material of the SOL Escape bivy seemed to handle moisture the best, it still had moisture buildup on the inside every morning. While this moisture buildup wasn't nearly as extreme as if we didn't have any shelter from the rain and snow, it's still alarming to wake up with a moist outer sleeping bag shell.
Selecting the Right Bivy
Each product in our Bivy Sack Review does something well but has some qualities that aren't designed or ideal for other situations. To figure out which might be best for you, you will need to consider the terrain you will be camping in, how hard the product will be abused, the weather protection needed, and weight you want to carry. Any extra feature creates added bulk and weight, decreasing the benefit of moving from a tent to a smaller bivy. General sleep habits should also play a part in the comfort of the bivy and your overall enjoyment of the product. Are you a light sleeper, or are you able to crash out in any crowded and cramped space, or do you prefer open air and arm space to toss and turn? Do you have fun nerding out on the lightest and smallest pack you can make, or do you prefer comfort? Maybe you're just looking for backup protection to throw in the bottom of your pack for when your adventure ends up taking longer than anticipated and puts you in a situation where sleep and dry clothes are a long way away.
Sierra Designs Backcountry Bivy one of our favorites from this year's lineup.
Where Will You Be Taking It?
A bivy sack can be a wonderful product because of its versatility. Whether high in cold mountains or in a summer meadow, a bivy provides a lighter weight alternative shelter. What you are sheltering from becomes the variable to consider before choosing the best product for your needs. Will mosquitoes be in full bloom? Are thunderstorms predicted, or even likely? How warm (or not) are the temps predicted to be, and how much warmer will that sack make a sleeping bag? We've broken down the most important metrics for scoring the ideal sack and discuss them in our review, as well as which environments are ideal for each one in the individual product reviews.
Bivy, Tent, or Tarp?
The first thing that draws people to a bivy sack is the idea of a lighter and less bulky tent. But there is active debate in the ultralight hiking community about whether a bivy, a tarp, or an ultralight tent is the best solution for those seeking lightweight and the smallest packed size possible. For two or more people, an ultralight tent or a lightweight backpacking tent will usually make more sense than bivies for each individual.
Augmenting With a Tarp
Types of Bivy Sacks
Commonly, these products come in a few different styles:
Types of Bivies
In our review, we examined four different bivy sacks to find the one that performed the best overall. We focused primarily on weatherproof models with reliable construction. Bivies typically come in a few styles:
These bivies are designed to disappear into your pack only to emerge when an unplanned bivy is necessary. The Frog TACT Bivy is the best example of a semi-reusable, inexpensive, emergency bivy. They protect you during critical times when shelter is needed, but can't necessarily be relied on to provide shelter day after day because of durability and functionality reasons. The SOL Escape Bivy however, blurs the lines of an emergency bivy and the next category of a minimalist bivy.
Ultra lightweight, simple, and constructed without poles or extra features that increase weight and bulk, three-season minimalist models are ideal for most applications. If you are an occasional backpacker who is looking to shed some weight, and you don't usually take trips in the winter or during raging thunderstorms, this is the model you will most likely want. These models offer protection from occasional weather and insects in the lightest and smallest packages available. And bonus, they are also usually reasonably priced. An example of this style in our test group is the MSR AC Bivy or the highly featured Sierra Designs Backcountry Bivy.
These are highly weather-resistant models, such as the Outdoor Research Alpine Bivy. They typically have some form of wire or pole to keep the fabric off of your face and are generally made of very strong materials to increase its durability and withstand repeated abuse. These can be used year-round and are ideal for winter camping or in situations where protection from the elements is essential. They are typically heavier than minimalist models, but usually more comfortable, especially when the weather is bad or temps are low. These models are normally more expensive than other bivy types. The price can rival that of a one-man backpacking tent. However, a bivy is usually still lighter and more compact than a tent.
While bivies are a stand-alone product, we always recommend adding a few items for any overnight camping trip, such as a sleeping pad and an appropriately warm sleeping bag, to increase comfort and allow for a safe night in the event of unforeseen weather or chilling cold.
If you have recently wandered into an REI, you will know there are about one million different sleeping pads available. For the sake of this article, we advise using a pad that matches your mission and bivy you have decided to take. We always lean towards the inflatable pads as they offer a better nights sleep without the hip pain. A valuable tip for those traveling in pokey territory with inflatable pads, put 3-5oz of Stans tubeless bike tire sealant into your sleeping pad. It is incredibly effective at sealing the little desert pokes without having to get out the repair kit. The lighter model bivies should be paired with lighter pads, while four season and winter bivies like our Top Pick for Weather Resistance winner the Outdoor Research Alpine Bivy are best paired with a warm and durable model that can hold up in similar terrain. For more information on sleeping pads check out our Best Sleeping Pad Review.
Some companies make lightweight pillows and fleece-covered stuff sacks. We prefer the lighter options, typically covering a climbing rope with a soft shell jacket or throwing a down coat over a pair of hiking boots. Those looking for a more luxurious camping experience might want to upgrade to a stuff sack lined with fleece, which can be turned inside-out and filled with soft clothing, or even a "camp pillow" built with either goose down or an inflatable bladder. As with any choice, if it is going on your back, consider the weight, as these luxury items have a habit of adding ounces fast. Don't miss our Best Camping Pillow Review.
Matching a sleeping bag for the bivy and weather expected will give you the best chances to sleep comfortably through the night. These days there are infinite sleeping bag options that boil down to down or synthetic and temperature rating. If you have an ultra-warm bag with tons of loft, make sure it will fit inside the bivy you're going to take! Some of the emergency bivies such as the SOL Escape are fairly snug and are probably only suitable for three season sleeping bags. Others such as the Outdoor Research Alpine Bivy can handle any sleeping bag. Other considerations are how much precipitation you are expecting as synthetic bags typically perform better in wetter environments. For more ideas on sleeping bags check out the Best Ultralight Sleeping Bag Review.
Tips for a Great Bivy
Don't Pitch in a Ditch
While this advice might seem a bit like old news, it's more important now than ever! As night starts closing in and your eyes get heavy from hiking all day, it's important to select your campsite with an eye towards potential hazards. Be cognizant of pitching in a low spot for water collection. Sleeping at high altitude puts extra stress on your body and makes it hard to recoup. This is sometimes unavoidable but if 30 minutes more of hiking gets you down a few thousand feet, your body will thank you! Often times very low bowl-shaped areas can become cold sinks, have you ever noticed the cold difference between the lowest part of a meadow and 100 ft up the ridge? One last consideration is deadfall. Make sure you camp far away from dead trees that have the potential to fall in the middle of the night when the wind kicks up. If camping in bear country, it's highly recommended, if not required in some areas, to pitch your bivy (or tent) at least 100 yards from the kitchen and the bear canisters.
Save Pad Weight
Part of the bivy sack program is doing whatever you can to save weight. Choosing a bivy is choosing to sacrifice some comfort while retaining protection from the elements. How far can we take the savings? Well, half pad options exist for most styles of sleeping pads and they ring in at a hefty weight savings. While the most rugged individuals can suffer through one night of sleeping on a half pad, others find it difficult to sleep. Make sure you experiment with the pad you will be taking on your next adventure and keep in mind how much more fun you will have if you get a good nights sleep and don't need a hip replacement the next morning.