The Essential Guide to Ultralight Bivy Sacks

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.

Hunkered down in a cave just north of Young’s canyon, UT | Katabatic Sawatch 15 combined with a MLD Superlight Bivy | Southwestern Horseshoe, February, 2012.

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.

Outdoor Research Highland Bivy Sack – 32 oz (photo from REI.com).

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.

Katabatic Bristlecone Bivy – 7.5 oz (photo from Katabaticgear.com)

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.

The Titanium Goat bivy on a snowy Pacific Crest Trail in 2011 (photo from Greg “Malto” Gressel).

  • 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.

During a 400 mile (644 km) route across Bolivia’s Altiplano region in 2017, a combination of the Katabatic Sawatch 15, Katabatic Bristlecone bivy and my layers, helped keep me warm in temperatures that regularly dropped down to 0°F(-17°F).

  • 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.

Uma Thurman would have had no issues dealing with the “claustrophobia factor” of bivvies | Kill Bill Vol.2

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 BackpackChances 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.

Borah Designs Ultralight Side Zipper Bivvy (photo from Borahgear.com)

Suitable Environments

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.

During the traverse of Southwest Tasmania in 2016, I combined the MLD Superlight bivy with an MLD Solomid XL.

Not-so-suitable Environments

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.

Camping in the dunes of Sandwood Bay | Final night on Scotland’s Cape Wrath Trail | On this particular trip to Scotland I took an innernet rather than a bivy as I was there during the height of midge season.

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:

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.

Beartooth Range, Montana | This shot was taken the morning after riding out a huge storm under the HMG flat tarp and Katabatic Bristlecone bivy.

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.

Sangre de Cristo Traverse, Colorado | September, 2016 | Most of this route along the crest of the Sangres was above tree line. During the trip I weathered some very heavy storms. Everything turned out ok, but if I was to do the route again, I’d take a Mid shelter instead of a tarp to combine with the bivy.

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.


Comments

The Essential Guide to Ultralight Bivy Sacks — 20 Comments

  1. Cam,

    Have you ever tried the MLD Bug Bivy or Bug Bivy 2? I use the Bug Bivy with a tarp in summer and love it. Lots of netting and height make it more like a mini net tent. Thinking about getting the Bug Bivy 2 for colder/wetter trips. Curious if you have any feedback on it. Thanks,

    Stu

    • Hi Stu,

      No, I’ve never used one of Ron’s bug bivvies. The original looks like a good option for hotter temps.

      For the recent trip to Scotland/Norway, I used an innernet in combination with the Duomid.

      Cheers,

      Cam

    • I was thinking bug bivvies needed a mention here. I recently ordered a Borah Bug Bivy as I’m most often in milder temps. All the lightweight and flexibility benefits above minus condensation issues.

      • Despite their name, personally I don’t consider “bug bivvies” to be “bivvies”, which is why I didn’t mention them in the article.

        I might be in the minority on this (which is fine), but to me a bivy offers some sort of weather resistance (be it wind, rain or splash), in addition to providing a sanctuary from bugs.

        • Fair point. I did think the context of your article was clear and technically that definition of bivy is probably correct. For me, I’m primarily a hammock guy in my areas but wanted an occasional lightweight ground setup. I started exploring tarp and bivy setups but realized a bug bivy was probably the best solution for my general conditions. So there was some logical overlap: functionally it was all exactly the same, only the material construction of the top changed and made more sense for my conditions. In my travels it was just working along points of a spectrum; how much or how little protection the system offered, all with the same basic setup.

          Regardless, thanks for the article since if I generally like my setup I’d be happy to invest in a true bivy for colder/windier conditions. Always enjoy solid recommendations.

          • No worries. Thanks for the messages. I could definitely see how a “bug bivy” (aka bug net with an attached floor 😉 ) would be a good option given certain conditions.

            In regards to your hammock comment, I’ve been thinking of giving them another try in the near future. I think they are an ideal option for rainforest /jungle areas. Unfortunately, despite numerous attempts, I’ve never been able to develop the knack for sleeping in them overnight. An hour long mid-afternoon siesta is usually all I can manage.

            • Yeah, my foray into hammocks was unplanned. In the early 2000s I was looking to ditch my too-heavy 2P tent and simply wanted a light solo shelter. One thing led to another and I ended up with the Hennessy Ultralight Backpacker. At the time there were few (if any?) solo shelters sub-2 lbs. and no other hammocks like it on the market (pre hammock boom). It’s been a brilliant piece of kit that I still have (and is still very competitive). I must say it’s liberating searching for a site when the ground is a non-factor. And I love the near-zero impact on my chosen site. As for comfort it’s funny: I’m a stomach sleeper at home and know that I shift around at least a few times a night. But once in my hammock, on my back, something tucked behind my knee, a slight shift toward one side and I sleep soundly straight through and I barely move, if at all. I think the way the fabric conforms to my body results in fewer pressure points. And I’m sure you know this, but, of course, a proper camping hammock that provides the diagonal, flat lay is key. Alas, after some years, there were some niggling design issues with the Hennessy that led me to purchase a Warbonnet Blackbird this summer when they went on sale; it directly addresses those issues. Summers are stupid hot here and the temps are just now cooling down for me to take it out for a spin. Hope you find something that works (trying different designs may help, there are some killer ones out there these days); there are lots of pros in the right setting. Cheers.

            • Cam – do you have any ideas for a more adaptable bivy design? I make my own gear, and would very much welcome your input…

              For long trails I’m playing with something versatile to go with my A-frame tarp. I like simplicity so would prefer a single do-it-all solution without having to worry about swapping out my bivy as conditions change.

              There will be times when I just want to use the groundsheet, times when I want wind and splash protection with decent venting, and times when I want bug protection with the maximum ventilation.

              I think that this can be achieved by making a bathtub floor with snaps along the side. When it’s calm and bug free, I can just use the floor on its own.

              I would also have a net with solid side walls that were high enough to provide good wind and splash protection. In bad weather, I’d snap it onto the floor so that the walls would extend to their full height with the netting providing venting at the top – looking something like the MLD Bug Bivy 2, which is basically just a better vented bivy with solid side walls.

              When I wanted bug protection with maximum venting, I’d snap on the net at a higher level so the solid walls were tucked under my mat and the the sides were all netting. It would be easy to adjust the height by gathering up any excess at the attachment points with a loop of bungee cord.

              You’d enter by unsnapping one of the sides. The snaps would be much more reliable than any zip.

              When detached from the floor, the net could provide some bug protection when eating or pooing on the trail.

              I’ve done a small prototype, and it only takes seconds to change from on setup to another. The weight penalty over a conventional bivy is pretty much insignificant.

              What do you think? Can you suggest a better approach?

              • Hey Geoff…….Thank you for the detailed message. You’ve obviously put a lot of thought into the “all-in-one” bivy design. I have to say, it sounds good. How many snaps are there in total? If you have a photo that you’d like to share, by all means send a link……Cheers, Cam

                • Hi Cam

                  This is where I got the idea:

                  https://youtu.be/Q4ECBP-AIn0?t=508

                  I need to experiment, but I think he has 4 snaps up each side.

                  https://youtu.be/Q4ECBP-AIn0?t=315

                  We’ve had a chat and he says it works fine. He has a tendency to over-engineer a bit – I think my implementation would be zipless for reliability (a bit more hassle to get in and out, but I’m normally only doing that once a day). And his tarp is HUGE. But this should give you the idea.

                  This setup would add a few grams of weight, but I think that the extra flexibility would more than compensate.

  2. Good review of bivies! Hey, I didn’t see my DIY Tyvek bivy bag that I made this season on your list? 😎 It was an epic fail upon first use. Yuuge condensation, and forget about side sleeping and adequate ventilation. I have since modified, but yet to re-test w the new mods.. may just need to shop from your list next time.

  3. I’ve used an MLD bug bivvy for the triple crown trails and it worked well with my quilt, but wind has always made for chilly nights. You’ve sold me on getting an ultralight bivvy. Sounds lighter than my current plan for cold weather which is just bring 2 quilts. Thanks for the wisdom!

  4. Another consideration, for me at least, on the choice between silnylon and DCF for the bottom is the feel of the fabric. Sil is slick and I slipped and slid on it a lot. I did get used to it after awhile, but during the summer I got a Borah bivy with a DCF floor and because it’s less slippery, it’s just a little less fiddly, which I really appreciate. Worth the coin, IMO.

    • A common problem with tent floors, too. One easy solution is to paint a few stripes on the floor with seam sealer. Tarptent has a YouTube video on seam sealing that shows the process, for those unfamiliar.

    • I’ve used the MLD and Katabatic models with the Therm-a-Rest NeoAir Xtherm (5.7 R-Value), and they both provided plenty of room.

  5. Is it an option to roll the bivy up in the morning with the quilt and deflated pad inside? Or is it just way too bulky? Would make camp setup and takedown a breeze…

  6. Nice roundup as always.

    I’ve grown increasingly fond of my MLD bag liner as a minimalist bivy. 2.8 oz, no zips or hood, so it’s quite a bit easier to get in and out of than a full bivy. The lack of a hood can be compensated by a hooded windshirt or bug headnet as conditions dictate. Much less condensation than my TiGoat bivy.

  7. Thanks for posting this Cam!

    I’m curious about sizing up. I’m 6′ and 155lbs.

    MLD mentions the medium size Superlight Bivy is good: FOR USERS: Up to 6’2″ / 185lbs. Are you still suggesting to size up to 6’6 if we are 6′?

    • I’m 6’1″ and 180 lbs. I’ve tried both the medium and large sizes of the Superlight (as well as Katabatic’s Bristlecone), and personally speaking I feel much more comfortable in the bigger models. It’s only a weight penalty of 0.5 oz to size up, and I’ve found the extra space to be well worth it for the reasons I allude to in the article.

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