Expedition Essentials: The Bivvy Bag

2 November 2023

The humble bivvy (bivouac) is a firm favourite of people sleeping under the stars who need to be weight and/or space conscious. From military to mountaineers, bivvies can be seen in various forms across the world. Typically, a bivvy refers to a temporary, improvised camp using man-made or natural shelter materials. Anything from highly technical materials such as Gore-Tex and Dyneema tarp to tree branches and rocky ledges. Two mainstays of bivvies are the bivvy bag and tarp. These can come in various forms and a broad range of price tags. It is easy to get confused about what is needed or what best suits your needs.

Bivvy bag

Your bivvy bag is what separates you, and your sleeping bag from the outside world. With some careful planning, it can protect you from some wild conditions, albeit with some discomfort thrown in for fun.

There are a few things to consider, the fundamentals are:

  • Space
  • Access
  • Protection
  • Breathability


Space is an essential consideration when buying your bivvy bag. In summer, you will rarely sleep in many clothes, your sleeping bag will be light and thin, and environmental conditions will (hopefully) be on your side.

It is recommended that you always have head-to-toe coverage; most bivvy bags will offer this, but it is worth double-checking, especially if you’re tall.

The next consideration will be the bag’s overall volume or circumference. The further you stray into 3,4 or 5 season territory; you will need more space for your sleeping bag and any additional layers you like to wear.

Bigger bivvy bags sometimes offer the opportunity to place your sleeping mat inside the bag. This has obvious benefits if you move in your sleep, are on sloping ground, or are in poor weather conditions.  Unless you are significantly impacted by weight or space, you could simply consider bigger to be better.

However, some bags verge into one person tent territory, these may have one or several hoops and ground pegs. These bags will provide even more space, especially if you zip them up most of the way. This design will significantly increase the weight and space requirements along with cost. You will also need to ensure the pegs and hoops do their job otherwise, you have a very loose and flappy bivvy bag.


The access point on bivvy bags varies significantly, you may find a smaller opening at the top of the bag or a zipped opening stretching over a third of the way down the bag, often called a ‘clamshell’ opening. This will influence the gymnastic effort required to shimmy yourself and your sleeping bag to the bottom of the bivvy bag.

Bigger openings may have some drawbacks in very wet and windy conditions, but this can be easily mitigated with quality zips, storm flaps, and some careful thought around your shelter.

Bivvy bags with a smaller opening may only have an elasticated drawcord like those on a sleeping bag. These bags will be harder to get in and out of and may close less than those with a zip, so the rest of your shelter and environmental conditions will require consideration.


Your bivvy bag will form a significant part (sometimes all) of your protection from the outside world. This may be the ground underneath you and the weather above you.

As with a tent, part of your bivvy bag represents a groundsheet. At the very least, this should be waterproof and, ideally, a ripstop fabric. Some bags will have a ‘bathtub’ design featuring tougher materials on the floor and side with lighter materials over the top.

Some designs, such as military bivvy bags, often constructed solely of heavyweight Gore-Tex, are incredibly tough and have a very safe feel, but the weight and space of these bags are significant.


It is very rare to find a bivvy bag that breathes perfectly, and if it does, it is likely to offer much less waterproof protection.

Overall, premium materials will breathe better and effectively address the balance of breathability vs. water resistance. Even with your head poking out of the bag, your body will still lose water, which will transfer to the inside of the bag at night.

You should remember that bivvy bags rarely breathe as well as a person. It is not recommended to close any bag completely; a fully closed bag may pose a significant danger to your health.

Assuming you are using a bag for more than one night, there are many things to consider here. Premium material should function better and reduce condensation build-up. Synthetic sleeping bags maintain performance when damp, so maybe a better choice. Do you need to factor in time to dry your sleep system and expose it to the sun? What can you do to perfect your layering and sleeping bag selection prior to and during the trip?


Most people are familiar with everyday plastic tarps used in a range of settings across the world. These do provide shelter but are not what we are discussing here, they are too big, too heavy and do not store well in rucksacks.

Camping tarps are made from lightweight fabrics such as nylon, polyester and Dyneema, which are often coated to give waterproof properties, much like tent fabrics.

Things to consider here are:

  • Size
  • Strength
  • Weight/packability
  • Attachments/fixing


You can go as small as 2.4m x 1.4m, this will provide cover for one person, but there will be restrictions on height and overall shapes you can use. A 2.4m x 2.4m tarp will give you much more height, offer versatility in the way you pitch, give greater coverage in poor conditions and more space for kit and movement.

Taps can sleep one person or multiple. Consider whether you travel solo or with friends/family and what impact this may have on your choice.


Most tarps are robust, and they will typically not take too much abuse apart from the weather. Ensure that fabrics are ripstop in case of any snags on trees or rocks and that any eyelets or tie points are appropriately reinforced.

If you do go for a super lightweight option, ensure you are checking the overall instructions and that it meets your needs.


The size and fabric thickness of your tarp are going to be the two key factors here. Given that you are choosing a tarp and bivvy bag over a tent you have already significantly reduced weight and pack size, so unless you need to push into the realms of extreme weight saving it may be worth prioritising other factors.


You need to pitch your tarp, which will have either a combination or series of eyelets and tags that can be tied with cord to various anchor points and supports.

Fixing points in the corners and along each side is essential. Ideally, there will be some fixing points in the middle of the tarp to support a pitched setup.


Double check that the fixing points are sound and sturdy before you pack your kit.


Bivvying gives you a highly adaptable, lightweight, and easy-to-use setup. You can use a bivvy in almost all the world’s environments. Given a little consideration, you can find the perfect setup for your needs.

A few of our favourite bivvy bags:

A few of our favourite tarps:

→  Test out your new Bivvy on one of our Extreme Medicine Courses!

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