Intrigued by the prospect of cutting your pack weight, sleeping warmer, and getting closer to nature? Trading your tent for a bivy sack might be the right move for you. Bivy—short for bivouac—sacks are ultralight shelters that range from emergency sleeping bag covers to weatherproof, one-person homes away from home. Here’s how to know if a bivy will work for you and, if so, how to choose the best one. 

In this article, you’ll learn:

• What to expect from a bivy sack
• What activities and camping personalities are best suited to bivy sacks
• The pros and cons of sleeping in a bivy
• How to choose among different bivy styles, sizes, degrees of weather protection, and features

What exactly is a bivy sack?

A bivy is, essentially, a protective cover for your sleeping bag; slide it on, then climb inside and catch some Z’s. The simplest ones are just sacks that slide over your bag, adding emergency shelter from the elements, while the fancier ones have a bit of structure and headroom. They typically have a durable, waterproof floor and a lighter, water-resistant or waterproof fabric over the top to keep precipitation out while letting some body heat escape. 

Who needs a bivy sack?

These minimalist shelters tend to be popular with anyone who wants to drastically cut pack weight: Think big-wall climbers, ultralight solo backpackers, bikepackers, and mountaineers who want to move fast and light in the high elevations. Some people pack simple bivy sacks as emergency insurance in case they’re stuck out on an unplanned overnight, while others happily camp in higher-end versions for weeks on end. Could one be right for you? Consider the pros and cons.

Pros

First and foremost, bivy sacks are very lightweight—between about 6 ounces to a shade over a pound. They pack down very small. They also add a few degrees of warmth to your sleeping bag, are very easy and quick to set up, and they let you camp in small, narrow spots (like rocky outcroppings or thick forests) where a tent wouldn’t fit. And devotees love that they make you feel more connected to nature; sleeping in one is the next best thing to sleeping under the stars, immersed in your surroundings.

Cons

Bivy sacks are so light and packable because they’re very small, which can make some people feel claustrophobic. And they have varying degrees of breathability, so you might end up dripping with your own condensation. Bivy sacks are truly just for sleeping: You won’t have any room to change clothes, read, or store gear. This can be a huge drawback in foul weather, making you wish you had a tent to hang out in while a storm batters you as you lie inside a bivy. 

Interested, but concerned about staying dry and comfortable? Some campers swear by a bivy sack paired with a tarp for extra weather protection and venting options without adding much more weight.

How do I choose the best bivy sack?

Think you and a bivy sack are a match made in heaven? Consider these factors as you shop. 

Style

Bivy sacks fall along a spectrum from emergency covers to fairly comfortable mini-shelters. An emergency bivy is usually just a water-resistant bag that slides over your sleeping bag; they’re the lightest and cheapest option, but also the least comfortable, so they’re usually only used in a dire situation. 

The next level up has water-resistant or fully waterproof/breathable upper fabric and might have extra features, such as full zippers or mesh covers for your face. These are a bit more comfortable and work as something you’d sleep in on purpose, not just as an emergency solution. 

All-season or year-round bivy sacks typically have a hoop or poles that prop up the fabric around your face, giving you some headroom and space to sit up. They’re usually durable, waterproof, and breathable, making them much better for riding out bad weather. These shelters weigh a bit more than their stripped-down counterparts, and cost more, too.

Size/cut

Some bivy sacks are very trim, while others have a bit more room. Your best bet is to get inside one before you buy it. Is it too confining? Do you have enough space for your feet and shoulders? Also make sure your sleeping bag will fit inside it. Some bivy sacks might compress a very lofty bag. 

Also consider how you get in and out of the bivy. You’ll have to crawl into a simple slide-on bivy, which can be tricky, particularly in wet weather. Entry and exit is a lot easier with bivvies that have some headspace and full-length zippers. 

Weather protection

Check the upper fabric. A water-resistant one won’t protect you from a downpour, but will breathe a bit better. A fully waterproof fabric is a better bet for wet conditions, but you’ll probably deal with some degree of condensation. Also look at the other features that affect weather protection: Does the bivy fully close with a zipper? If so, does it have a storm flap? How does it close? A bivy with a drawstring or flap closure, for example, can let leaks in.   

Breathability

This is particularly important if you run hot and/or you expect precipitation. Waterproof/breathable fabrics will be most comfortable to sleep in. Look for full zippers and mesh panels that lend venting options. 

Features

In addition to the features noted above, you might also want a few other extras. Bug netting is a great feature to keep biting insects at bay while still letting you see the stars. Also consider bivy sacks with reflective inner fabric for added heat or those with internal straps to keep your sleeping pad in place.

All articles are for general informational purposes.  Each individual’s needs, preferences, goals and abilities may vary.  Be sure to obtain all appropriate training, expert supervision and/or medical advice before engaging in strenuous or potentially hazardous activity.