For hikers that enjoy tarping and cowboy camping, ultralight bivy sacks represent an excellent supplementary option for your sleeping system. Weighing in at between 4.5 and 7.5 oz (0.13 – 0.21 kg), they add approximately four to eight degrees of warmth, pack down next to nothing, and help to keep drafts at bay when you turn over in your quilt during the evening.
Over the past decade I have used ultralight bivvies – in combination with a tarp – for hundreds of nights in the backcountry. Environments have ranged from California’s High Sierra to Bolivia’s Altiplano to the rugged wilderness of Southwest Tasmania. What follows is my take on the hows, whys and wherefores of bivvies for backpacking.
A Tale of Two Bivvies
There are two main types of bivvies. The most commonly known to Jill and Joe Public is the traditional model, which is a stand alone, waterproof shelter, that normally weighs in somewhere between one and two pounds (0.45 to 0.9 kg). These models sport mosquito netting and usually a hoop to keep the bag off your head. For hiking purposes (as opposed to climbing or mountaineering), I’ve never been a fan of this type of bivy for the following reasons:
1. Rain – During sustained periods of precipitation, traditional bivvies present a number of issues including: A. They feel claustrophobic; B. Not easy to go for a leak without you and your stuff getting wet; C. Changing clothes can be an exercise in contortionism, and ;D. Cooking can be problematic.
2. Weight – They aren’t that light. For example, they are heavier than not only all the tarps I have used, but also the Mid-style shelters as well. Note that there are some stand-alone bivvies that with a just sneak under a pound from Mountain Laurel Designs and Borah Gear (Note: The latter doesn’t come with a hoop, while the MLD Soul Bivy does come with a mini hoop that keeps the bag a few inches off your face).
3. Condensation – It has been just over a decade since I last used a traditional bivy sack. It was a Gore-tex model from Outdoor Research. I experienced condensation issues pretty regularly. If you are keen on trying a stand-alone bivy, go for one with 3-layer eVent material on top. The main difference between eVent and Gore-tex is that the former doesn’t have a polyurethane inner coating, which means it breathes a little better. For a detailed comparison of eVent and Gore-tex see the Go Outdoors Blog.
The second type of bivy – the Ultralight Bivy Sack – weighs considerably less than traditional models (i.e. normally between 4.5 and 7.5 ounces depending on the materials used), has a waterproof bottom, a water resistant/ breathable top and a bug net window. The UL Bivy is not a stand-alone shelter and is normally used in combination with a tarp.
Benefits of the Ultralight Bivy
- Splash protection: When used in combination with a tarp, they help to keep rain splatter and groundwater off your sleeping bag when it begins to pour down.
- Warmth: They add four to eight degrees of warmth to your sleep system. For example, on the CDT in 2012, I came through the San Juans of Colorado in late September. Despite temps that were regularly down to the high teens/low twenties F, I stayed warm in a combo of my Katabatic Palisade 30 quilt and an MLD Superlight bivy (Note: I am an “average” sleeper (neither hot nor cold).
- Draft Protection: Bivvies are like a wind shirt for your sleeping system. Their warmth to weight ratio is excellent, and they keep the drafts at bay if you happen to turn over in your quilt during the evening.
- Small Footprint: The small footprint of bivvies (along with the fact that there are no pegs or guylines to worry about) means you can pretty much camp anywhere. This can be a real boon at the end of a 12 to 14 hour day in rugged terrain, when the last thing you really want to be doing is rooting around looking for the ideal camp spot.
- Cleanliness: The help to keep your bag cleaner, which over the long term can help on the durability front.
- Insect Protection: Bivy’s keep tiny critters, both terrestrial and volant, at bay if you’re sleeping under the stars or a tarp.
- Organization: I’m one of those people that tends to spread their stuff out upon arriving in camp. A bivy helps organizationally challenged folks such as myself keep items such as a headlamp, beanie, water bottle and other such items close at hand during the evening.
- Tossers & Turners: If you have trouble staying on your not-quite-wide-enough sleeping mat when out in the boonies, a bivy will help keep you aligned, as you and your sleeping mat don’t have anywhere to go.
- Quicker Setup & Departure: The lack of pegs, guylines and poles, means a quicker setup and take down of camp.
- Associated Weight Savings: The extra warmth provided by a bivy sack, means that you can take a lighter sleeping bag (e.g. a 20F quilt, rather than a 15F quilt), leave the groundsheet at home, and carry a smaller/easier to pitch tarp (e.g. a 9×5.5 to 9×6 or even 7, as opposed to a 10×8). This equates to a total associated saving of between 5 and 6 oz (i.e. 3 oz quilt; 1 to 1.5 oz groundsheet, and; 1 to 1.5 oz tarp).
- The Space Factor: As mentioned above, UL bivvies aren’t meant to be used as a stand-alone shelter. They form an UL combo with a small to medium sized tarp (basically anything smaller than 9×7). And therein lies the biggest advantage they have over traditional models; the feeling of space. When it’s pouring down with rain you don’t feel like you are stuck in a coffin, thanks to the fact you have a tarp overhead plus a bug net window to peer out of when you shut up shop.
Limitations of the Ultralight Bivy
- Not a stand-alone shelter
- Privacy – If you are looking for privacy, you are better off going with a tent as opposed to a bivy and/or tarp.
- They can feel claustrophobic: This is mainly a factor for stand-alone bivvies in the rain. That said, if you get an UL model that’s too tight or has a tiny bug net window (e.g. MLD Superlight), they can also feel quite restrictive to some folks. When it comes to bivvies, you should always size up.
- No Space for your Backpack: Chances are you will only have enough space inside your bivy for a few items you may need during the night (e.g. headlamp and beanie), plus your sleeping mat and quilt. Generally speaking, I put everything else inside my backpack, which I then place under my feet (Note: Having your feet a little higher than your head helps to reduce swelling in the lower extremities after a long day on the trail).
- Condensation: Ever since bivvies were first invented by alpinists looking for weather protection for their sleeping bags on big multi-day ascents (especially on large walls), the main drawback for many folks has been moisture build up inside the bivy.
Minimizing Bivy Condensation
- Campsite Selection: Try to avoid camping close to water sources or on valley floors, where katabatic air will sit of a morning. Whenever practical, look for an elevated location, as a little breeze can also go a long way when it comes to negating the effects of condensation (and bugs). See the Youtube video below for the full skinny.
- Don’t sleep in wet clothes and avoid breathing into your sleeping quilt or bivy.
- Low Hung Branches – Sleeping under low hanging branches means less condensation and a warmer night’s sleep thanks to a reduction in radiant heat loss. The down side is the views aren’t as good. You can’t have everything. Example: When I hiked the first 600 miles of the Hayduke Trail in Feb/March of 2012 as part of the Southwestern Horseshoe, on most days just before dark, my hiking buddy (Mike “The Gambler” Towne) and I would be on the look out for stands of Juniper trees to sleep under. In addition to meaning less dew and additional warmth, they also acted as a natural wind block – no small thing on a cold, windy and exposed Colorado Plateau during winter.
- Unzip and Hook up – The goal is to to maximize air flow/ventilation. Whenever practical, try to leave your bivy somewhat open. When sleeping under a tarp, utilize any bungee loop ties near the head and feet, to try and keep a gap between the quilt and bivy thereby enhancing air flow.
- Don’t carry a quilt that’s too warm – The more you sweat, the more likely it is you will encounter condensation. Don’t overdress when going to bed, and whenever possible take a quilt or bag that’s temperature-appropriate for the conditions in which you are hiking (Note: Flexibility in regards to temperature range is one of the big advantages quilts have over bags. This particularly holds true for models such as Katabatic’s Flex series).
- Bandanas & Midday Breaks – Condensation is a bit like shit, sometimes it just happens. Take solace in the fact that it’s more of a nuisance than a major issue. In such situations, the best thing you can do is to shrug your shoulders, and have a wiping material handy just in case things get too drippy. If your bivy and sleeping quilt are damp when you pack up camp, give them both a shake, and then stop when you have the opportunity and dry them out in the sun.
Materials & Design
- Top – Breathable / Water Resistant Fabric – Examples include Argon and Pertex Quantum. Note: As with any DWR treated fabrics, eventually the effects of dirt, grime, weather and body oils, will take their toll on the material rendering it less water resistant.
- Bottom – Waterproof: The two options are silnylon and DCF (cuben fiber). The former is heavier, cheaper and more durable. The latter will save you one to two ounces in weight, set you back an extra US$70 in price (using the MLD Superlight as a yardstick), and most probably won’t last as long.
- Zipper – Chest or Side?: Go with the latter. For a negligible weight penalty (less than an ounce), it makes the bivy easier to get in and out of, as well as making a difference on the ventilation front.
- Hang Loop: Positioned over or near the face to keep the bug net off your noggin.
- Size-up: Don’t be tempted to save an ounce by going with a size that’s just big enough (e.g. If you are 6′ tall, go with a long 6’6″ model). Trust me on this one. A bit of extra space translates to more freedom of movement and more head room when you tie off the bivy to a hang loop or branch.
- Bug Net Size?: Opinions vary on this point. Basically it comes down to a combination of personal preference and the conditions in which you will be doing most of your bivy-toting trips. For example, if you are heading out into what is likely to be windy and rainy conditions, then a smaller bug net window will offer more protection from the elements. If inclement conditions are very unlikely, then you may prefer a larger bug net window which will help minimize condensation and provide you with less of a closed-in feeling.
As a general rule of thumb, the UL bivy / tarp combo works well in arid regions (outside the scorching summer months), and relatively dry mountain areas (e.g. Sierra, Rockies, Wind River Range, Pyrenees, Alps, Atlas, and the Andes). I’ve also used the combination successfully in ranges such as the Appalachians in the shoulder and winter periods, when the heat and humidity of summer has abated.
Additionally, I’ve paired the UL bivy with a fully enclosed mid-style shelter (outside of bug season) in cold and wet environments such as the UK, New Zealand and Tasmania. In regards to this particular example, most folks will prefer a innernet over the bivy, due to the likelihood of rain and/or boggy terrain.
In hot and humid weather (e.g. Appalachians in July and August), bivvies can be clammier than a guilty man’s handshake. In such conditions you are better off using a tent, hammock or even a big bug net with your tarp.
During the height of bug season in places such as Scotland (midges – late June to September), Alaska / Lapland (mosquitos – mid June to end of July), and the West Coast of the South Island of New Zealand (sandflies – December to February), save your sanity and leave the tarp/bivy combo at home. Take a tent instead.
Bonus Bivy Q&A
What are currently the best options for UL Bivvies?
All models mentioned below have side zippers, and the first figures listed are for silnylon floor versions:
- Mountain Laurel Designs Superlight Solo (7 oz or 5.5 oz DCF Floor)
- Katabatic Bristlecone (7.5 oz )
- Borah Bivy (7 oz or 4.35 oz DCF Floor)
- Titanium Ptarmigan (6.4 oz)
How do they compare?
I have extensive experience with the MLD Superlight and Katabatic Bristlecone models over the past decade. Both are similar in regards to weight, performance and durability. The main difference is in the bug net windows. MLD offers two options: 1. A small half moon model which is not for claustrophobics, and; 2. An all net hood, which is definitely better on the ventilation front, but offers less protection when the weather is coming in. Katabatic offer just the one bug net window option, but personally I’ve always felt the size is just right (i.e. not too big, not too small. Come to think of it, they should change its name from “Bristlecone” to “Goldilocks”).
I haven’t personally tried the models from Borah or Titanium Goat. In regards to the latter, my good mate, Greg “Malto” Gressel, has used his TG model for the past seven or eight years and it’s still going strong. As for the Borah model, I know Andrew Skurka has used the silnylon floor version in recent times. In regards to the DCF model, it’s certainly uber-light and the folks over at Ultralight Reddit generally give it a double thumbs up, but the jury is still out in regards to it’s long term durability.
Do I Need a Groundsheet?:
No. That said, a piece of polycro, tyvek or a mylar space blanket weighs only 1 to 2 oz, and will help to preserve the bottom of your bivy for longer. This especially holds true for models that have a DCF bottom, which when it comes to abrasion, don’t do as well durability-wise compared to silnylon. In short, I’d recommend the following – if you use a DCF model, take a groundsheet, if you use a silnylon model, leave the groundsheet at home.
How do you deal with Bugs?:
As previously mentioned, bivvies aren’t ideal during the height of bug season. That said, sometimes bugs can make cameos at other times of the year as well. Here are a couple of suggestions as to how you can deal with them:
- Tie-off Techniques: If using your tarp, tie off the top of your bivy to one of the loops on the inside wall. If cowboy camping, use some bungee cord to connect your bivy to an overhanging branch or even a hiking pole or two (i.e. strapped together in duopod mode). These are the moments when you will most appreciate having upsized your bivy; the extra space can be a sanity saver.
- Campsite Selection: If you know a buggy night is on the cards, it behooves you to find a breezy spot. A bit of wind is like kryptonite to sandflies/midges/mosquitos, and can be an absolute godsend when the little blighters are really swarming.
- What about wearing a hat?: You may have heard this one before. In theory, the brim of the hat keeps the mesh off your face at night. The trouble is, it only works for folks that sleep on their backs, and even then it doesn’t give you much more than a tiny amount of space.
My Favourite Thing about UL Bivy Sacks is……..
Cowboy camping. Bivvies enhance my experience sleeping under the stars. They act as a draft-stopper when I turn over at night, provide me with an extra four to eight degrees of warmth, keeps the bugs at bay, and provide a little extra buffer time, just in case it unexpectedly starts to rain and I quickly need to set up my shelter.
When I first started using UL bivvies more than a decade ago, I remember thinking they were well worth the relatively small weight penalty for the extra versatility they provided my sleep system. After hundreds of nights using them in the backcountry later, my opinion remains unchanged.