Can You Suffocate in a Bivy Sack

Bivy sacks in a campsite

Bivy sack may be the right choice for you if you want to cut down the weight on your next hiking or camping trip. You may also be keen on cutting your sleep system weight down. Weight reduction notwithstanding, there are important issues you need to tackle before making the decision. Like what to do with the elements and whether a bivy can provide adequate protection from rain and cold.

But what about safety? Many campers want to know whether you can suffocate in a bivy sack.

There is no scientific evidence to support the assumption, but there is a high risk of having major problems with condensation or even suffocating in your sleep. However, there are basic recommendations to help you make the most of your backpacking trip. 

In this article, we cover the main advantages of sleeping in a bivy sack, but also the potential risks you need to consider before you give it a go.

Table of Contents

What’s a Bivy Sack?

If you lack backpacking experience, you might need to learn about the key characteristics of bivy (bivouac) sacks. Simply put, bivy sacks are a lightweight covering that protects a solo sleep system. They were initially intended for climbers and mountaineers who need compressible, lightweight protection from inclement weather.

In the recent couple of decades, bivy sacks have undergone important modifications. They’ve become much lighter, quite sturdy, and waterproof. Therefore, they’re ideal for lightweight hiking or backpacking trips.

Even though bivy sacks are fit for different purposes, they specifically come in handy when bivvying in rainy and cold weather. They can also add up to approximately 10 degrees of warmth. This should ensure a good night’s sleep, which seems to be essential if you’re s physically active during the day.

How to Pick a Bivy Sack?

Now that you’ve read about the key characteristics of bivy sacks, let’s take a look at how you can pick the right one for your needs. But before we move to important issues you need to consider before buying a bivy sack, we will explain the types of bivy sacks you can find in the market.

When deciding which type of bivy sack you actually need, you should undoubtedly focus on the bivy’s structure, size/weight, fabric, and openings.

Traditional vs Ultralight Bivy Sacks

Traditional or “stand-alone” bivy sacks (bivy shelters) are typically waterproof and weigh from 1 to 2 pounds (0.45 to 0.9 kg). They also have mosquito netting and a hoop that provides extra room above your head and keeps the sack from falling.

Stand-alone bivy sacks add up warmth to your sleep system, provide a standalone all-in-one shelter, and are fairly comfortable. On the other hand, they may feel claustrophobic, they are heavy and need a ventilation solution because of condensation. They also provide little or no protection if you’re getting in/out during heavy precipitation.

Ultralight bivy sacks are substantially lighter (4.5 to 7.5 ounces), depending on the material used. These sacks cannot be used as standalone shelters and are commonly combined with tarps. They come with a waterproof bottom, a breathable, water-resistant top layer, and a bug net window.

Ultralight sacks can add up to 8 degrees of warmth and you can easily set them or break them down. However, they’re not fully waterproof, also have a claustrophobic “vibe” to them, and problems with condensation.

Whatever model you decide to purchase, make sure it has ventilation options. Make sure it’s waterproof. You should also opt for sacks with zippers in the side to be able to vent out moisture. This will help you with condensation and keep you dry in the morning. A mesh panel or a net bug window will help you keep the bugs out.

Things to Consider When Purchasing a Bivy Sack

  • Structure. If you’re a restless sleeper and need a bit more room, you should definitely pick a structured bivy sack. There are extra headspace and breathing room. On the other hand, non-structured bivies are perfect for situations when you just need shelter from the elements. Like extreme elevations.
  • Size/weight. Fabric undoubtedly determines the weight of your bivy sack. Therefore, you should do some research to pick the right size and weight. Being a typically minimalist choice, sacks come in various ultralight options. Campers and backpackers alike opt for bivy systems because they require minimal storage space.
  • Fabrics. Bivy sacks typically come with different types of fabrics. Given its purpose, the floor fabric is heavier and sturdy, whereas the top fabric is breathable, lighter, durable, and waterproof. Being confined in a sack, you’ll soon understand the importance of breathability. To avoid waking up wet from condensation, we recommend opting for materials that will help reduce moisture.
  • Openings. There are many models with openings available for those who lack comfort in fully enclosed models. To handle bugs while you sleep, you can pick a model with a mesh covering.

The Dangers of Sleeping in a Bivy Sack

There is a considerable level of risk for people sleeping in fully sealed bivy sacks. There are actual reports of people suffocating in their bivies. Regardless of whether the cause of death is verified or not, the assumption was that these people died of asphyxiation.

In this article, we cover the possible reasons behind the assumption, but they are hypothetical as there is insufficient scientific evidence to support this.

  • You should avoid full enclosure in your bivy in sub-freezing temperatures. The water vapor will freeze in the bivy and on the bivy fabric, thereby making it completely air-tight.
  • If in above-freezing temperatures, the breathability of the fabric may not allow enough air exchange to support respiration. Take this for example – with a cotton bag or clothing, you can breathe easily even if you pull them over your head. But if you try with a breathable fabric, like Gore-Tex or Momentum, you will have to inhale/exhale really hard to get air to move through the fabric. And this may not be enough.
  • The breathability may also be affected by water vapor condensing on the surface in above freezing conditions. You will not be able to breathe through wet cotton. Moreover, condensation on the breathable fabrics may obstruct the diffusion of air. Breathable fabrics are more hydrophobic than cotton, but the put if you try with a breathable fabric, like Gore-Tex or Momentum, you will have to inhale/exhale really hard to get air to move through the fabric. And the pores may be saturated with vapor.

Tips to Stay Safe in a Bivy Sack

  • You should never (ever!) fully enclose your head in a bivy bag, regardless of the specification saying it’s breathable. This practice of full enclosure has resulted in many documented cases of deaths.
  • If using your bivy in winter, a good idea may be to use just use a fleece hat or full-face balaclava to protect your ears from the wind and keep your head warm.
  • Consider packing a one-man tent, in case you realize that you’re not fit for tarp life. It will save your weekend and you can also use it as a security blanket.
  • When picking a bivy sack, opt for a design that makes suffocation a non-issue. All the same, breathing into a bivy is not a great idea as the vapor in your breath will condense and leave you soaked. That’s why you should leave an opening and check recommendations from the manufacturer.
  • Make sure your bivy sack has a mesh covering/bug net window, especially if the weather is warm and moist and there’s a potential for bugs. Needless to say, you won’t need a mesh screen if you’re camping in snow caves or high altitudes.
  • Pick a traditional tent instead of a bivy sack if the weather is too cold and you need room for food preparation.
  • Check if the size of your bivy sack is enough for your foot-box, hood, and ultimately, your body. If not, you’ll be tossing and turning and uncomfortable and spend even more air.

Person next to bivy sacks

Tips for Sleeping Well in a Bivy Sack

There is a high risk of having a hell of a night in your bivy sack (or even suffocating or experiencing major problems with condensation). Nevertheless, to make the most of your backpacking trip, you should follow the basic recommendations.

  • Sleeping mat: using a sleeping mat will help you keep your body heat instead of losing it through the ground.
  • Water-resistant sleeping bag: highly recommended to prevent condensation from forming.
  • Setting up: Pick an area of flat ground that has no sharp objects and is not in the path of animals and other humans. It should be safe for night sleeping and will not flood if it rains.
  • Tossing and turning: Use straps to prevent your bivy from rolling. Alternatively, you can use flat elastic straps and glue velcro material on the middle ends and each end to the bivy base.
  • Pack Items: Depending on the size of your bivy sack, you can stuff the items around you, or leave them in your waterproof bag protected by your rain pack cover. This will probably not work in heavy rain which is when you should use a large pack liner. Keep your food inside or hang it up in accordance with conditions.
  • Handling moisture: You are highly recommended to leave the headcover off, except when it rains or snows. The ventilation potential is critical. Even if it rains, you should leave a small opening. Even the breathable materials, like Gore-Tex or similar never actually breathe the way you expect them to.
  • Sleeping on snow: pick a safe place for the night, avoid avalanche paths or trees loaded with snow. The condensation may freeze overnight and make the fabric of your sack less “breathable”.

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