Ultralight Bivy Sacks 101

Ultralight Bivy Sacks 101

Ultralight bivy sacks are used by backpackers for cowboy camping or under floorless shelters, such as tarps or pyramids, to protect their sleeping bags/quilts and sleeping pads from wind, insects, mice, and other creepy crawlers. Most are not waterproof and function more like sleeping bag covers encapsulating a sleeping pad and sleeping bag or quilt, with mosquito netting over the head and face for insect protection. They’re very different from heavier-duty waterproof bivy sacks used for winter camping or mountaineering, like the Outdoor Research Alpine Ascent Bivy, or the Rab Ridge Raider Bivy, which resemble mini-tents with collapsible rods to make them more livable in harsh weather.

Ultralight Bivy Sack under a floorless Dyneema DCF Tarp
Ultralight bivy sack under a floorless Dyneema DCF Tarp

Most ultralight bivy sacks are sized for use with a sleeping pad and a sleeping bag or quilt. But sleeping in them really isn’t as claustrophobic as it might look. There’s still plenty of room to sleep on your side or prop your head up on your arm to read at night. Bivies with side zipper access are also a lot easier to get into and out of than ones with front openings where you need to slide in feet first. This is particularly true at night when you’re feeling especially stupid and uncoordinated.

Ultralight Bivy Sack under a floorless pyramid trap
Ultralight Bivy Sack under a floorless pyramid trap

Many ultralight bivy sacks have a cord loop that you can tie to the underside of your shelter to hold the bug netting up off of your face when you sleep. You can also tie this cord to the rafters in a trail shelter and use your bivy to protect you from bugs and mice. Your bivy sack also provides a wee bit more privacy inside a shelter if you want to change into your long underwear.

When sleeping under a flat tarp or catenary cut tarp, a bivy sack helps protect your sleep system from splash-back, which occurs when rain bounces off the ground and under your tarp and on your sleeping gear. This can be an issue if you have a narrow rectangular or catenary cut tarp but is less of a concern if you use a wider one, whose sides are staked close to the ground in bad weather.

Using a bivy sack in a shelter. Cabot Cabin - White Mountains
Using a bivy sack in a shelter. Cabot Cabin – White Mountains

Most ultralight bivy sacks don’t impart much extra warmth to your sleeping bag or quilt at night, maybe 5 degrees tops, although they will block a breeze from chilling you. They are often made with a top fabric that is quite breathable to help vent any condensation build-up at night. In very hot weather, you can use the top fabric of a bivy like a sheet for sleeping. Some ultralight bivy sacks are available that are all mesh for use in warmer weather use, but the norm is part mesh and part solid fabric.

Tarping in the Pemigewasset Wilderness
Tarping in the Pemigewasset Wilderness

Ultralight bivy sacks are quite delicate pieces of gear made by hand and must be treated gently if you want them to last. If you buy a bivy sack that has a zipper, it’s good to lubricate it periodically with Gear-Aid Zipper Lubricant so it doesn’t snag, and to dry your bivy sack out after every trip you take to avoid mildew. If you see black mildew spots begin to form on the bivy fabric, washing your bivy sack out with Revivex Odor Eliminator will eliminate the mildew and prevent damage to the fabric.

Recommended UL Bivy Sacks

Make / ModelWeightOpening
Katabatic Gear Pinon Bivy7.3 oz / 207gTop
Katabatic Gear Bristlecone Bivy7.3 oz / 270gTop
Borah Ultralight Bivy5.0 oz / 142 gChest
Borah Cuben Bug Bivy4.2 oz / 119 gChest or Side
Mountain Laurel Designs Superlight Bivy5.5 oz / 156 gSide
ANDA Burrito Bivy5.6 oz / 158 gTop

Why Would You Use an Ultralight Bivy Sack?

So far we’ve discussed what an ultralight bivy sack is, but not why you’d want to use one. There are basically two reasons: tarp camping (for gear weight reduction) and wilderness immersion.

Tarp camping with a flat tarp, a catenary cut tarp, or a pyramid tarp is lighter weight than using a tent, even an ultralight Dyneema DCF tent from the likes of Zpacks or Tarptent. You still need some sort of insect protection under a tarp and at 5-8 oz, a bivy sack weighs significantly less than an inner tent or net tent, making it possible to carry a complete shelter system that weighs under a pound.

In addition, sleeping in an ultralight bivy sack is a much more immersive way to experience the wilderness than sleeping inside a tent, with walls and a floor. If you cowboy camp in a bivy sack or sleep under a tarp, you’ll feel much closer to the environment surrounding you.

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10 comments

  1. Great article! Tarp and bug bivy has become my favorite shelter system. Fyi, all of Borah Gear’s bivys are available with both chest or side zips. ?

  2. Great article. I’m planning a trip and want to go as light as possible and still have a shelter.

  3. Honestly, when I’m out and about in the countryside I actually enjoy closing up my little tent at night. I’ve had night attacked by mosquitos and ones with rats and mice scuttling about unnervingly, and it’s just nice to know no small critters are getting to you.

  4. You nailed it. But the really interesting considerations are when you start to treat all the kit together as a shelter and sleeping system rather than indivual pieces
    E.g. a tarp+bivy+mat+floor can weigh more than many single layer tarp tents unless really careful and getting high quality gear
    E.g. if raining hard, a larger tarp might be needd, which can add up to more than a small tent – but give you more room if stuck in it for a long time – but not if you have to be inside your bivy. So pros and cons.
    E.g. the entire system including sleep bag should also be considered in cooler weather – for an enclosed tent can be warmer and allow a lighter bag and pad than a small tarp. Unless you use a larger tarp and peg to the ground to stop drafts.
    Ie lots of variations, not just weight of indivual items, and trying the combos out to dial in your comfort to the weather

  5. There’s something really nice about being able to lie down in a tiny flat space in my bivy! I usually miss having it on at least one night when I choose to bring a tent instead. It is light enough, including a tarp, to bring two systems when I take a grandkid backpacking.

  6. In a bivy, with no tarp or other type of roof above, it’s great to wake up and see the stars above your head. You truly feel much closer to the great outdoors in a bivy!

    • It seems that is the great race to the bottom (in terms of ultralight gear) that people have forgotten that the point is wilderness immersion and not how many miles you can do in a day or how fast.

  7. I really love the bivy/tarp combo in the Smoky’s where I will probably have to sleep in a shelter (bivy keeps out mice) but might also end up outside which is where the tarp comes in

  8. To get rid of any condensation within my bivy I use always a vbl. First a silk liner, then the vbl, then the sleeping bag or the quilt, and at last te bivy.

    The silk liner is drying within minutes when I get up. And the sleeping bag or quilt is always dry.

    And, you don’t need a breathing bivy this way.

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