Does A Bivy Sack Add Warmth?

To save weight on your next backpacking trip you may be considering a bivy sack over a traditional tent. I love the idea of possibly cutting my sleep system weight down but let’s answer some important questions before making the decision. A big one has to do with the elements and how a bivy will handle rain and cold.

So, does a bivy sack add warmth? Bivy sacks do add warmth. They are designed in such a way that they add approximately 4 to 8 degrees of warmth to your sleeping system. In addition to warmth, bivy sacks naturally keep drafts away since they fully enclose your body. Even the most restless sleepers who toss and turn will be kept protected from the elements.

If you are new to backpacking, you might be wondering what bivy sacks actually are. Bivy sacks, which are also called Bivouac sacks, are a protective covering that provides solo backpackers a lightweight sleep system.

When bivy sacks were first put to market, they were designed mainly for mountaineers and climbers. The main idea was for them to have lightweight and highly compressible protection from bad weather for emergency purposes.

Since then, bivy sacks have come a long way. Today, they are much lighter, more durable and made out of waterproof fabrics. This makes them perfect for lightweight backpacking trips.

When you brave the outdoors, you never know how mother nature will treat you. You might have pleasant weather on the start of your adventure and then face continuous rain or wind at any point.

It is at these times when bivy sacks come in handy as they can keep you safe from the rain and add up to potentially 10 degrees Fahrenheit of warmth. You’ll be able to have a good night’s sleep, which is crucial when you have to remain physically active the next day.

How to Choose a Bivy Sack

Now that you know what bivy sacks are, let’s take a look at how you can choose the right one for you and your trip. But before we discuss the considerations you need to evaluate when buying a bivy sack, let’s see the two types of bivy sacks available in the market.

Traditional Bivy Sack Models

The bivy sacks sporting the traditional design are called ‘stand-alone’ sacks. These models are usually waterproof and weigh somewhere around 1 to 2 pounds or 0.45 to 0.9 kg. They also come with mosquito netting and a hoop at the area above your head. This hoop is added to keep the bag from falling on your face.

Pros

  • Hoop to keep the sack from resting on your face/head
  • Warm
  • Has bug netting
  • Comfortable
  • Standalone shelter in one unit

Cons

  • Can feel claustrophobic
  • Lack of protection getting in and out of sack during continuous rainfall
  • Heaviest of bivy sack types
  • Must be proactive about ventilation to reduce condensation

‘Ultralight’ Bivy Sacks

Compared to the traditional bivy sack, ultralight models are considerably lighter, weighing approximately 4.5 to 7.5 ounces. The weight can slightly differ depending on the material used. Unlike traditional bivy sacks, the ultralight designs are not standalone shelters and are often used in combination with a tarp. This adds additional security against rainfall.

In addition, ultralight bivy sacks also come with a waterproof bottom, a bug net window, and a water-resistant and breathable top layer.

Pros

  • Can be used in combination with a tarp to keep water at bay
  • Add up to 8 degrees of warmth
  • Small footprint
  • Lightweight
  • Facilitates quicker setup and breakdown

Cons

  • Not a standalone shelter/fully waterproof
  • Can feel claustrophobic
  • Condensation problems similar to traditional models

Both traditional and ultralight bivy sacks have their own advantages and disadvantages. The one you choose depends on a few considerations you need to make before purchasing one.

Pre-Purchase Items To Consider

Make sure the model you are considering has ventilation options. If there is any potential for rain on your outings – the bivy sack should also be waterproof. Check if the sack has zippers in the side that you can open up to vent out moisture. This will minimize condensation, saving you from waking up in a wet and humid sleeping bag. If you’re going somewhere that has potential for bugs, make sure the bivy sack has a mesh panel or net window to keep them out.

The weight of the bivy sack:

The weight and compressed size of the bivy sack are important considerations, especially for lightweight or ultralight backpackers. One key reason campers choose bivy systems is that they require less storage space than a regular tent. A heavy or bulky bivy sack would be counterproductive.

Where you’re going:

If you are going to camp someplace where the weather will be warm/moist/potential for bugs, make sure that the bivy sack you choose has a mesh panel over the face to keep them away. On the contrary, if you’re camping in snow caves or a very high altitude, mesh screen won’t be as important.

The temperature and climate:

The temperature and climate conditions of where you’re going will determine if just a bivy sack will be appropriate. If the weather is too cold and you require room to prepare food and dress ‘indoors’, you’ll want to consider a traditional tent instead.

Your body size:

Check the shape of the foot-box, hood, and the overall size of the bivy sack to make sure you don’t feel like you are wrapped in a tight space. If your shoulders are broad, you won’t be able to toss and turn properly. Also, consider your sleeping style – stomach, side, back etc. Will your position be comfortable in a close quarters bivy?

Are Bivy Sacks Truly Waterproof?

Whether you want to use a traditional model or the ultralight, bivy sacks are designed primarily to perform the following two basic functions:

  1. Keep the sleeping bag dry
  2. Increase warming capacity

Based on this… Yes, bivy sacks definitely come in waterproof options. Typically, they are made out of durable-grade nylon that is coated with urethane, which makes the fabric waterproof. This material is the same one that most manufacturers use for making tent floors.

The bottoms of modern bivy sacks are made out of this nylon material, which keeps water from seeping into the bag. This comes in handy for snowy campsites or when it has just rained.

As for the top tier of the sack, it is made out of ripstop nylon. This material is lighter than the one used for the bottom tier. In some models, it is also covered with Gore-Tex material, which is a breathable laminate material that waterproofs the top tier.

While bivy sacks keep water from getting into the sleeping bag in most situations, you can face some trouble if there is sustained rainfall. Bivy sacks have an opening at the top for breathing. You may need to cover it with a tarp to keep the rain from coming in.

Bivy Sack Vs Tent for Lightweight Backpacking

Bivy sacks and tents have both been long used by campers. In fact, some campers take both kinds of shelters for more extreme outdoor activities and severe weather conditions. Each has its own advantages and disadvantages.

I have made a list of pros and cons for each below. Based on your needs and priorities, you can evaluate which one is more practical for your adventure.

Bivy SacksTents

Pros

  • Very lightweight
  • Can be camped anywhere
  • Fast setup and departure
  • Closer to nature
  • Adds warmth
  • Waterproof options

Pros

  • More space
  • Comfortable
  • Water and weather-proof
  • Less condensation
  • Suitable for multi-day trips
  • Sleep more than one person

Cons

  • Fits just one person
  • Condensation due to small size
  • Can make you feel claustrophobic
  • Air drying between nights on multi-day trips
  • Footwear and backpack likely left outside shelter

Cons

  • Heavier and take up more space
  • Lightweight tents are expensive
  • Larger footprint/harder to find setup spots
  • Longer set up and departure time

Based on the pros and cons of each mentioned above, bivy sacks are more suitable for lightweight backpacking. But if your needs surpass that which just a bivy sack can fulfill, a tent might be a better choice.

In the end… Make sure that you do your research to find the right manufacturer and type of bivy sack for your personal requirements. This will be crucial to keep you comfortable and make your trek a successful one.

Related Questions:

Do you need a sleeping bag with a bivy? You will only need a sleeping bag with your bivy if the overnight temperature justifies it. If you are camping in a location where it gets very cold at night, take one. In warmer climates, however, you can skip the sleeping bag and sleep in the bivy sack with a sleeping pad underneath you and an extra layer of clothes.

Is a cuben bivy good for snow camping? A cuben bivy is perfect for certain types of snow camping. They are designed to be lightweight and waterproof. With an adequately warm sleeping bag and pad, you can be nice and toasty.

 

Related content: How to Waterproof a Hiking Backpack: The Complete Guide

Does A Bivy Sack Add Warmth?

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