Everything you need to know about bivy bags
Life is an adventure, it's not a package tour. Eckhart Tolle
A bivy bag (aka bivvy sack) is a waterproof jacket for your sleeping bag. Sometimes spelt ‘bivy’, sometimes ‘bivvy’, both these terms are short for ‘bivouac’ meaning a temporary (usually minimalistic) shelter. They are thin, lightweight and compact, making them a lot smaller (and often cheaper) than a tent. Being so small, it’s possible to sleep almost anywhere with a bivy, including small patches of clearing, rock faces and so on. Hence, they are generally considered a more flexible shelter option than a tent. Like tents, bivies come in four-season varieties making some models suitable for alpine conditions (e.g. Outdoor Research Alpine Bivy).
There is no perfect shelter and bivy bags are not perfect. One disadvantage of a bivy bag is that you are likely to get some condensation forming on your sleeping bag as there is very limited air flow. This is ok if you can easily dry your sleeping bag out, but not ideal for extended trips in wet conditions. The other consideration is comfort: in undesirable weather, you can bunk down in a tent with a cuppa, where a bivy is small and closed area. Depending on the design some bivies are not great in heavy, sustained rain or in areas with lots of mozzies as some have a simple opening for your head at the top with no insect screen. Each bivy bag design is different and some deal better with these issues then others, so it is worth keeping an open mind about their potential.
Check & pack Checking and packing your bivy
Bivies are relatively simple to check and pack. Most setups are simply one piece of material, similar to the outer material of a tent. Some have a small set of poles and perhaps pegs as well, and in which case, follow the same procedures to check and pack these as you would do for a tent.
In general, the key things to check are:
- Are all the parts there?
- Are the seems intact and waterproof?
- Does it work, and is there any damage?
- Is it clean? Some gear may pose biosecurity risks if dirty, as there is a risk of transmission of diseases, pollen, spores, seeds and so on into uninfected regions.
- Do you have a repair kit for that part in case something breaks in the field?
Even weight distribution and ease of access are key concerns when deciding how to pack your bivy (or indeed any items in your backpack). Since a bivy is only needed at camp, it’s generally packed near the bottom of your pack, but make sure you can access it in rain without getting your gear soaked.
Depending on the bivy design, the material may be relatively heavy, so aim to get it near to your back. Since the bivy is soft and flexible, consider using it as padding between hard bulky objects to stop them moving around (e.g. stove, gas, billy). Ideally, waterproof the bivy as you want to minimise the risk of your sleeping bag getting wet when slipping inside the bivy. Your sleeping bag is the most important thing to keep dry, and since it comes into close contact with the bivy, it’s worth spending time wrapping it in a dry bag or bin bag to keep water out (most manufacturers provide a lightweight waterproof covering). Avoid packing the bivy in a way that creates direct contact with sharp objects (e.g. edges or poles, pegs) as they may tear the material. Wrap lightweight waterproof cover around it (usually supplied by manufacturer).
Chapter photo by Allysse Riordan on Foter.com / CC BY-NC-SA
Use in Field Using your bivy in the field
In dry weather conditions, using a bivy bag is easy. Choose a flat area free from pointy rocks or roots, that will not flood in rain and clear of other risks such as falling tree limbs. Lay out the bivy bag and slip in your sleeping bag. Larger bivy bag will also take you sleeping pad inside, but tighter fitting bivy bags may require you to have your sleeping pad outside. If the bivy bag has poles or guy lines secure them in place. With open topped bivy bags, close up the gap using the to a small gap leaving plenty of room to breathe. You can even do the set up (sleeping bag into bivy) at home before setting out and just unroll the whole bivy-sleeping bag set up in one.
Consider laying out a groundsheet and setting up a tarp over the top. This helps protect your bivy bag and helps to keep your gear dry in rain. There are lots of different options, so play with it and find what works well for you on your trip.
Practice using your bivy at home first. This means you become familiar with all the material and how everything fits together. Remember you’ll be tired after a day of walking and it’s nice to be able to know how your tent fits together, rather than having to figure it out for the first time in the field!
If you haven’t used your bivy for a while, you can test if it’s still waterproof by setting it up in the backyard and using a hose to spray it with water. This is an easy way to determine if there are any issues (again, much nicer than finding out at 3am in the field!).
Remember that you are more exposed to weather conditions such as rain, wind and cool weather in a bivy than in a tent, so it’s worth taking additional clothing layers to stay warm. Also, think through where and how you’ll store all your other gear. Unlike a tent, where packs can be protected from wind, rain and animals, with a bivy bag, your pack will stay out overnight. Be sure to waterproof gear well and store food securely. Carrying a large heavy duty plastic bag can be a useful way to store your pack overnight.
In wet or windy weather, choose somewhere as sheltered as possible to set up your bivy. This could mean finding an overhang or sheltered clump of trees for windy protection. If the weather conditions are wet, place the sleeping pad inside the bivy bag for extra protection of the sleeping pad (if the bivy is indeed large enough to fit over the pad).
Chapter photo by moosepics on Foter.com / CC BY-NC-ND.
Care & Maintenance Caring and maintaining your bivy
For bivies, the main material maintenance is similar to care for the outer part of a tent. For bivies with pegs and/or poles, again, care and maintenance is essentially the same as for tents.
Cleaning and drying
The bivy is fairly prone to picking up mud and dirt on trips so it’s worth spending time cleaning it well when you get home and before packing it away in a long-term storage. Check that the material is clean by running your hands over both sides of the material and removing any mud, earth or sand using warm water and non-detergent soap. Check any zippers, guy lines and other attachments too.
Air out the bivy thoroughly (using indirect sunlight) and make sure it’s completely dry before packing away in a cool dry place. Never use artificial heat or direct sunlight to dry the material as this can melt or damage the materials.
Washing and improving breathability
Many bivy bags are constructed using breathable materials with a durable water repellent (DWR) treatment similar to quality raincoats. Read your bivy bag instructions for washing and reapplying the DWR. This usually means using a washing machine to apply the DWR and a tumble dryer to help set the DWR and improve the material breathability. This with rain jackets this a process that you may benefit from doing each year or so.
For bivies, the most likely repair you will need to do in the field is repair a rip to the main fabric. Remember to pack a repair kit for mending fabric (e.g. Coghlan’s Nylon Tent Repair Kit). Typically, your field repair kit will be small, with only those essential items necessary to make temporary in-field repairs. Back home, you can revisit your field repair and decide if you need to do a more thorough job.
Check that the sealant is still intact, and periodically apply DWR to the fabric.
Make sure that the fabric is clean and bone dry before storing it in a cool dry place. It’s a good idea to store the fabrics loosely to allow a small amount of airflow and prevent mildew buildup.
Selection Selecting a suitable bivy
Bivy bags are great lightweight shelters for bushwalking, with many different types to choose from. They are great options for people seeking a lightweight, smaller alternative to a tent. Traditionally used as an emergency shelter, bivies are now fairly common amongst the outdoor community, particularly for people that frequently need solo gear and are doing trips where weight considerations are critical (e.g. long distance walking, multi-day climbing etc). When used correctly, bivies can be just as durable and comfortable as tents, however, the type of bivy must be well matched to conditions you typically expect to use it in. If weight is the key concern, a bivy may be the answer, but bear in mind that some one-person tents these days are also extremely small, compact and lightweight (e.g. Zpack Duplex).
Modern-day bivy bags are typically made from two types of material: the underlayer made from similar fabrics to tent floors (e.g. durable nylon), and the upper layer made from a lighter weight waterproof and breathable nylon.
Some key considerations:
- Is a bivy appropriate for this trip? Will there be lots of heavy rain? Would I like to sit up and read/play cards? Can I share with someone else? If the answers are yes, it may make more sense to share a 2-person tent.
- Size: A bivy that’s too small also won’t be warm because the sleeping bag is pressed up against the wall, flattening insulation and making it less effective. A bivy that’s too big will have a lot of extra air space and won’t be easy to warm up (rarely a problem). Generally, a bivy that provides a little extra room is the best option, and you can store a few extra items there also.
- Tent-like protection above head: Some bivies have a larger section of fabric at the head (called ‘bivy shelter’ rather than a ‘bivy sack/bag’) which can be propped up with poles or a guy line to create a tent-like structure over the head and protect from rain and wind. It adds a small amount of extra weight, but may be worth it to make it easier to read and organise gear.
- Managing condensation: The biggest issue with bivies is the buildup of condensation due to poor air flow. Look for models that have breathable material, and ventilation options. You can also reduce condensation by airing during the night. Using a sleeping bag with a water-resistant shell can be helpful to reduce the risk of your insulation getting wet.
Some examples of bivies:
Another option that some bivy users prefer is to add an additional protection from rain via a tarp. This can be a great option in weather conditions when rain is expected.