What Is a Bivvy Bag and How Is It Different from a Sleeping Bag?

What Is a Bivvy Bag?

Also known as a bivy sack, a bivvy bag is a thin waterproof cover for your sleeping bag. It is used over the top of a sleeping bag to provide an additional layer of protection for you and keep your sleeping bag dry.

You can think of a bivvy bag as kind of a one-person tent as that's what they are, but smaller and cheaper. Additionally, it's very discreet and lets you sleep on flat ground, not protected from the environment as if you're in a micro tent. 

Like any other outdoor gear, a bivouac sack has the right time and place to use as it is very polarizing in terms of use and can be excellent in certain situations and horrible in others. They're not recommended for young children - our article about when kids can use sleeping bags will answer any questions you have on that subject.

A bivvy bag was initially to serve outdoor enthusiasts who need ultralight protection for their sleeping systems. 

They were initially a waterproof nylon shell and offered nothing more than that. It provides fast protection from wind, rain, or snow, which allows you to camp anywhere and in places where you couldn't imagine doing so with a one-person tent.

Since their invention, bivy shelters have evolved, and the technology has significantly changed, with more people worldwide, including the military using them for different purposes.

Types of Bivy Sacks

There are three different types of bivy sacks based on the amount of protection, structure, and materials.

Based on Protection

Limited Protection Bivy Sacks

Limited protection bivvies are simple nylon shells that provide essential protection. At the same time, you sleep to protect yourself and your sleeping system from water splashing when it's raining, or the wind blows a little bit.

Partial Protection Bivy Sacks

The partial protection bivvy bags are more robust than the limited protection bivy sack, usually made from Gore-tex. It's pretty heavier and offers more protection than a nylon bivvy bag.

However, the downside is that you can't cinch up the zippers 100% secure, which will allow bugs to crawl into the bag, making it not fully secured.

Full Protection Bivy Sacks

Full protection bivvies offer 100% protection from water, dust, and bugs. It's fully waterproof, and you can zip up the zippers 100% to prevent bugs and other insects from getting into the bag.

Based on Structure

Within the three types of bivy sacks based on protection, we have structured and non-structured bivy sacks.

Structured Bivy Sack

A structured bivvy bag has a structure to it and comes with a metal wire which you can pull away from your face. It's a little bigger, gives you extra headspace and breathing room which is great if you like a little bit of extra wiggle room.

Non-structured Bivy Sack

This type of bivy sack doesn't have a structure, and the material will lay on you if you're inside the bag. Non-structured bivvies are a bit smaller than the structured type and perfect when you reach extreme elevations and need to cuddle up to hide against the elements. 

Fabric

Most bivvies usually contain various materials, including nylon, Ripstop, and Gore-tex.

The floor fabric is the same fabric used in most camping tent floors and typically consists of nylon coated with urethane to make it waterproof. 

The upper part of the bivy sack has a lighter fabric, usually Ripstop nylon, with a breathable, waterproof laminate such as Gore-tex.

Nylon tends to be lighter, less expensive, and less breathable, while Gore-tex is generally the most costly and heavier due to its waterproof and breathable properties of Gore-tex.

Shapes and Designs

Bivy sacks are mostly like a slightly larger sleeping bag with a simple design and lie flat like a blanket. 

It has some features like stiffeners, guying options, or small poles, and the bag's volume results from our bodies or these features. 

They are primarily breathable, waterproof, and the extent depends on the materials used, as Gore-tex tends to be more waterproof and breathable than nylon. A big enough bivy sack will ensure that your sleeping bag loft is without restrictions, and the length will determine how well the bag can accommodate the sleeping bag to get well inside. 

There are bivvy bag models that offer additional headroom to provide relief when sleeping in them for multiple nights in a row. But these models are usually not 100% stable as some can only stand upright when the zippers are closed, while others tend to tilt towards your face when a slight breeze picks up.

Bivvies with complex constructions like the criss-cross pole structure found on the Carinthia Observer are more reliable, comfortable, and protected. However, they tend to weigh a little bit and are more expensive.

If you want complete protection, a total protection bivy sack comes with strong zippers that can completely seal up the bag's interior and prevent bugs and other elements from getting in and disturbing your sleep. 

Bivvies with drawstrings, vents, and hook-and-loop fasteners don't offer complete protection as they always leave small gaps and openings that can allow bugs and other elements to get into the bag.

However, it's easier said than done, and sealing yourself in a bivy sack will be primarily done in colder climates or higher altitudes. You'll be OK with a limited or partial protection bivvy bag in most situations and everyday bivouacking adventures.

Dimensions

Depending on your size and needs, the dimensions of a bivy sack play a vital role in comfort, as bivvies with extra length and volume are more comfortable in extreme conditions.

The dimensions of a bivvy bag vary from manufacturer to manufacturer, and it's essential to check and ensure that it meets your specifications.

A tight bivvy bag will require you to squeeze your sleeping bag into the bag, which will compress the filling in your sleeping bag, which will consequently reduce its insulation and ultimately affect its lifespan. 

Openings

The openings of a bivvy bag differ on every single model, and some are easy to get into while some are not.

Some models have side zippers that allow you to hop in from the side, while other models will have to crawl in from the front.

Pros & Cons of Bivy Sacks

Bivy sacks have significant advantages and disadvantages over wild camping with a tent. 

Pros 

• Lightweight: One of the most significant advantages of a bivvy bag over a small tent (even a one-person tent). Most bivvy bags are very light, weighing less than 500 grams. The lightweights of bivvy bags will make your camping experience more enjoyable as you won't have a weight that will slow you down or become heavy for you.
• Take up less space: Unlike camping tents, bivy sacks will take up a little space in your backpack and on the ground. You will find this beneficial in situations where you wouldn't have enough space to set up your tent, and it will make it easier for you to find suitable wild camping spots.
• Protection: A bivvy bag will help protect you from condensation, which is a big concern, especially in the UK, and also protects you from bugs and other insects.
• Cheaper: Bivy sacks are often more affordable, and you can get one for as low as $20.
• Add warmth: Bivvies are great for colder climates and can add as much as 10° to your sleeping system. The minimal air space inside the bag will make your body heat the bag much quicker, and you will feel warm much quicker. Adding warmth to your sleeping bag will help in the wintertime, and if your sleeping bag temperature rating is below the temperature of the environment you'll be camping in. 
• Quicker to set up: With no poles or guylines, bivvy bags are super easy to set up, and you can quickly set them up and hop in a matter of seconds, especially when you see the rain or wind coming in. This is great, especially for those looking to have fewer chores to do or when you are tired and want to set up your sleeping system quickly.

Cons 

There are many cons associated with bivy sacks, so you have to keep these in mind when planning your outdoor adventure.

• Although bivvies are very lightweight, this comes at a cost! Some bivy sack models lack something to keep the head panel off your face, which can be uncomfortable and sometimes frustrating.

• Bivy sacks are not suitable for bad weather and rainy conditions. You will have to use a tarp with bivvy bags during rain because everything inside will get wet once you open the sack. There's no way to crawl out of a bivy sack when it's raining without getting wet.
• Bivvies can add up to ten degrees to your sleep system, unsuitable for summer. It will make you feel hotter and sweaty, which will make you uncomfortable.
• Condensation: This is probably the most significant disadvantage of bivvies. No matter the type of material you have, it will not be 100% breathable, and you should consider this when purchasing one.
• It doesn't matter if it's in the summer or wintertime; you will probably wake up to a wet sleeping bag and a damp bivy sack. A wet bivvy bag is a unique problem that you need to keep in mind but will not be a big problem if you're going on an overnight trip. However, if you're going on a multi-day trip, you'll have to dry both your sleeping bag and the bivvy bag, which will take time away from your adventure.
• Zipping up a bivy 100% will keep bugs away, but that means your head will be inside the sack. When your head is inside, you'll release moisture that will accumulate on the bivy and make you uncomfortable. On the other hand, if your bivvy bag doesn't zip up 100%, you'll have to contend with bugs. So it would be best if you always kept this in mind before choosing to go camping with a bivy sack.
• Less space: Most bivvies are very confined, and there will not be enough room to fit in your gear, though you may have room for your cell phone and battery. You should consider this, especially if you've always spent your time sleeping in a tent and used to have plenty of room. It might take time before you can sleep in bivy sacks.

What Is the Difference between a Bivvy and a Sleeping Bag?

Both bivvy and sleeping bags serve different purposes, and one can not replace the other.

Bivvies don't offer the warmth and protection that sleeping bags provide, and be ready to stay frozen if you try to sleep in a bivy sack without a sleeping bag.

Though bivvies are larger than sleeping bags, they fall under the shelter category of keeping elements off you, while a sleeping bag is more about keeping you warm and comfortable.

Generally, bivvies are emergency shelters that you use in conjunction with a sleeping bag and are not meant to replace sleeping bags.

How to Setup a Bivvy Bag

I will show you how to set up a simple bivy sack that doesn't have poles and a two-pole system bivvy bag.

How to Use a Bivy Sack That Doesn’t Come with Poles

It is straightforward to set up this type of bivy sack. All you need to do is:

• Pull out the bivy sack from its pack.

• Roll the bivy sack out.

• Put your sleeping bag inside.

• You can have your sleeping mat by either placing it underneath the bivvy bag or inside the bivvy bag under your sleeping bag. Putting the sleeping mat inside the bivy sack will help reduce sliding and reduce the chances of punctures if you use an inflatable roll mat.

• Now you can get inside your sleeping bag and, after that, pull over your head, leaving a gap for your face.

• If your bivy sack has a drawstring, pull it tight around your face to flow warm air into the bag.

How to Set Up a Two-Pole Bivvy Bag

Below is a step by step tutorial on how to set up a two-pole system bivvy bag:

• First off, before you start setting up your bivy sack, you should choose an appropriate site that is clear of debris or sharp rocks that might puncture the fabric of your bivvy bag.

• Once you've found an appropriate site, you can pull the sack out of its pack.

• After that, you should start setting up the poles. There will be two different poles, a longer one and a shorter one. The longer one should go on inside the white sleeves at the opening.

• You should pass through the sleeve.

• After that, take the end piece of the poke and put it on each end. 

• Then find the corresponding snap with the white backing that goes with the white sleeve and snap it into place.

• Now take the shorter pole and put it through the gray sleeve on the outside (usually a little pole arrow indicator).

• Likewise, take the end pieces and attach them to the end of the pole, looking for the corresponding snap on the outside.

• You've finished setting up your bivy sack. Now take a look inside the bag, and you'll see two straps that you can use to keep your sleeping pad in place.

• Once you find the straps, undo the Velcro and put your pad inside to give the bivy sack structure.

• Now hold the pad in place and put the strap together.

A two-pole design bivy sack has a variety of configurations to choose from, and you can start by going for maximum ventilation and having the bivy sack wide open.

The next thing would be to utilize the bug netting, which you will be zipping up from inside the sack. You can also fold back the fabric so that the bivvy bag and poles stand straight up.

After that, the next configuration is to slightly tilt the overhead pole forward to give you extra protection against precipitation while keeping bugs out and getting enough airflow.

For further protection against heavy rain and storm, you can tilt the overhead pole over to close the outer zippers. However, you'll want to leave the outside zipper a little open, about six to seven inches, to allow fresh airflow throughout the sack.

Why Choose a Bivy Sack over a Tent?

There are conditions where bivvies would be a better choice over a tent. Here are some reasons why you should choose a bivy sack over a tent:

Lightweight

Most bivvies are very light, which is one of the top reasons why campers prefer them over tents in various situations. Tents are typically heavier, and if you're going on a camping trip and are concerned about weight holding you back, a bivy sack could be a good option.

Packable

Bivvies have an ultra-compact nature that makes them a valuable asset. You can pack them inside your backpack and your food and other camping gear. They are also easier to pack after sleeping or when you are in a hurry and want to pack your stuff quickly.

Warmth

Bivies add extra warmth and can trap in a few degrees of warmth (around ten degrees) and can hold heat better than a tent. Due to their smaller size, they can trap your body heat to add extra warmth to your sleeping bag.

Waterproof

Bivy sacks feature breathable and waterproof materials (nylon, Ripstop, Gore-tex) to prevent you and your sleeping bag from getting wet and reduce condensation. However, they are more enjoyable in fair weather conditions and winter.

No Setup Required

Bivvy bags are more accessible to set up and don't require any hassle. With no poles to assemble and pitching required, you don't have to worry about the setup or breakdown of anything the following day.

It Doesn't Take Up Much Space

If a setup space is a concern, choosing a bivy sack over a tent will be a good idea because it doesn't take up much space, and you can use it anywhere at your convenience. It is essential to consider this, especially if you're going on a group camping and there'll not be enough space to set up a tent.

When to Use a Bivy Sack

Bivy sacks are ideal for winter and colder weather because they add warmth to your sleeping bag. You will find this helpful in cold and frosty weather because more heat equals more comfort. Also, if you're camping in a place where the temperature rating is lower than that of your sleeping bag, using a bivvy bag can help bridge that gap to stay warmer at night.

When Not to Use a Bivy Sack

While adding warmth is a tremendous advantage in winter, it can be catastrophic in the summer when it's too hot. It's not a good idea to use a bivy sack in the summer and hot weather because despite the weather is hot, it will also add warmth which will make you sweat, feel uncomfortable, and unable to sleep, especially if you have a waterproof bag.

A camping tent would be ideal in the summer and hot climates, and this should be an essential factor to consider when choosing a bivy sack in the summer.

Frequently Asked Questions about bivvy bags

How Do Bivvy Bags Work?

Bivvy bags are like a waterproof jacket for your sleeping bag; they work as a tent and protect your sleeping bag from rain, dust, bugs and add warmth to your sleeping bag. They are lightweight, portable, easy to pack, discreet, and often cheaper than tents.

Do You Need a Sleeping Bag with Bivy?

Yes, bivvies are just a cover for your sleeping bag so you will need a sleeping bag with a bivy. Your sleeping bag goes into the bivvy bag, which serves as an additional layer of protection to your sleeping bag. People sometimes confuse bivvy bags with sleeping bag liners, but they're not the same thing.

Is a Bivvy Bag the Same as a Sleeping Bag?

No, a bivy bag is not the same as a sleeping bag, and both serve different purposes. The purpose of a sleeping bag is to keep you warm and comfortable in extreme weather conditions, while a bivvy bag is to protect your sleeping bag.

Can You Sleep in a Bivvy Bag?

Unless you want to stay cold or have a sleepless night, it is not a good idea to sleep in a bivvy bag without a sleeping bag. A bivvy bag is just a cover for a sleeping bag and doesn't have the features to keep you warm, safe, and comfortable while you sleep.