Emergency Blanket Vs Bivy

If you’ve ever considered ultralight hiking or backpacking, you’ve probably come across bivvy sacks as well as emergency blankets or emergency space blankets as possible avenues.

But are there any differences between them, and which one should you bring on your next adventure?

An emergency blanket is a thin, compact, and lightweight reflective sheet that can be used as a shelter from the wind and rain that also radiates some of your body heat back to you. A bivy is a more protected shelter that uses highly water-resistant or waterproof, durable, and breathable fabric to prevent moisture and wind entry but at the cost of being heavier.

Knowing the differences between these two shelters will allow you to make an informed decision about which one to bring with you the next time you go camping.

What Is A Bivy Cover?

A bivy cover/sack is an interesting piece of gear for a number of reasons. It is a kind of a giant sleeping bag that protects you from insects and the elements, but it can also be set up quickly and easily.

They are usually made of a highly waterproof, durable fabric that is breathable and prevents condensation while also allowing moisture (water vapor) to pass through.

Bivy sacks can be classified into two types: those with drawstrings and those with zippers. The drawstring bags are often on the cheaper end of the price spectrum, while zippered bags are more expensive.

As I mentioned, these bags are primarily used to protect against the elements, but they can also serve as a separate camping setup.

Bivy covers come in a variety of sizes and colors, and they can be made of various fabrics such as SilNylon or even Gore-Tex, which determines the bag’s insulation.

They are designed for use as an emergency shelter from rain and wind but can be used for other purposes such as warmth on cold nights when you don’t want your sleep system (sleeping bag, sleeping pad, etc) touching the ground.

What Is An Emergency Blanket?

Originally developed by NASA, an emergency space blanket is a pure aluminum foil sandwiched between polyester or polyethylene.

This reflective blanket is supposed to reflect back 97% of all radiated heat, making it an excellent addition to your survival kit in case you require additional heat into your system.

Despite the fact that these blankets are extremely durable, they are only designed to last a few uses. Furthermore, these blankets, like a bivouac sack or bivy sack, are very water resistant and effectively block off the wind.

Further reading: Can You Use A Space Blanket As A Groundsheet?

However, unlike a bivvy bag, these blankets are non-porous and will accumulate a lot of condensation from your breathing if used similarly to a bivy sack (covering up yourself in a space blanket and not around your sleep system).

In my opinion, one of the best ways to use a space blanket is as a groundsheet to reflect any residual heat back to you and prevent any further heat loss.

Also, in an emergency situation, such as hypothermia, having a space blanket in your first aid kit can mean the difference between life and death.

Difference Between An Emergency Blanket And A Bivvy

A bivy bag and a space blanket are both good options for minimalist camping, where you want to add as little weight to your backpack as possible.

If you’ve ever done a thru-hike, you’ll know that every ounce (oz) in your pack determines how far you can hike comfortably and easily, and both of these items are excellent candidates for the shelter you need during these hikes.

That being said, here are some of the most noticeable differences between them:

1. Weather Protection

As both bivy covers and space blankets are made from highly water-resistant materials, both of them are great at keeping precipitation such as rain or snow at bay.

That said, there are many bivvies available that are semi-water resistant and require additional waterproofing, such as a tarp set up around it.

Further reading: How To Bivvy In The Rain?

Space blankets, on the other hand, are completely waterproof because they are made of non-porous, non-breathable polyethylene/polyester sheets.

Since not all bivvies are 100% water-resistant, a space blanket is a better option in cases of heavy precipitation.

2. Breathability

Bivy bags tend to be more breathable and reduce condensation build-up far better than a space blanket.

The reasoning is that the more breathable fabric in a bivy allows the water vapor from your breath to be released into the air, whereas in a space blanket, it gets trapped and accumulated on the blanket, making you wet if it comes into contact with your skin.

However, not all bivies are breathable because some will accumulate moisture in the same way that a space blanket would, albeit on a smaller scale.

3. Insulation

A space blanket is a better heat insulator because most space blankets reflect back 90% or more of your body heat released through radiation, whereas a bivy can only add a few degrees of buffer temperature to your overall sleep system.

Having said that, a space blanket is only effective at reflecting back radiation heat and not conduction or convection. A bivy can insulate you from all frontiers (however low the insulation may be).

As a result, for camping in moderately cold temperatures, a bivy bag excels, whereas for cold weather camping, a warm sleep system (insulated down bag, high R-Value sleeping pad, and a space blanket) is preferable to relying solely on a bivy bag.

4. Comfort

Comfort is subjective and can vary from person to person. That being said, an emergency blanket will give you more space to move around if set up like a tarp, and wearing it around as a cloak isn’t uncomfortable either.

A bivy bag, on the other hand, is similar to a sleeping bag but allows for more movement. Either way, sleeping on a raw bivy or space blanket without any ground insulation isn’t the best option since neither is effective insulation against conduction through the ground.

As a result, it is strongly advised to use a sleeping bag/sleeping pad in addition to them for added comfort and ground insulation.

Curious read: Sleeping Bag Liner Vs Bivy Sack

5. Bug Protection

Bivy bags, particularly those with mesh around the hood, are the clear winner here.

As well as being highly breathable for use during warm seasons like summer or spring, they also prevent nearly 100% of all bugs from entering your sleeping system.

Space blankets do not offer any bug protection, and you may need additional bug spray to protect yourself from bug bites.

Having said that, a space blanket is not designed for warm weather camping anyway, so it is not their fault that they don’t have any bug protection.

6. Weight

Space blankets are the clear winner here, with some weighing as little as 3 ounces, which means you can get a set of 5 of these at the same time and still weigh less than a pound.

A bivy, on the other hand, can be as light as 5 ounces, but for a well-insulated breathable bag, the weight can be as much as 2 pounds.

7. Price

Similar to weight, a set of five space blankets can cost between $10 and $20, making them some of the most affordable survival gear you can get as a hiker/camper when hiking in harsh weather conditions.

A bivy sack, surprisingly, can be purchased for as little as $20, but a more robust insulated and breathable bivy with mesh for summer camping can cost as much as $300.

Table Of Differences Between A Bivy And An Emergency Blanket

Here’s a table summarizing the differences between them:

Features/Functions	Emergency Blanket	Bivy Sack
Weather Protection	Waterproof	Highly water-resistant; some can be completely waterproof
Breathable	Less Breathability; easily accumulates moisture	Highly breathable; less condensation build-up
Insulation	Reflects 90% or more of radiated body heat	Adds a temperature buffer of a few degrees to your sleep system
Comfort	Grants a lot of space; freely movable	Constrictive; but more roomy than a sleeping bag
Bug Protection	No bug protection	Mesh fiber that is almost 100% bug proof
Weight	Very lightweight	Lightweight; gets heavier with more sophisticated models
Price	Very inexpensive	Inexpensive; gets costlier with improved features

Space Blanket And Bivvy Alternatives

Here are some alternatives to a bivy or a space blanket:

Sleeping Bag Liner

A sleeping bag liner is a thin fabric that goes inside your main sleeping gear (sleeping bag, top quilt, etc.) and serves two purposes.

First, it keeps you dry by absorbing sweat and other bodily fluids, keeping your main sleeping gear clean and dry. And secondly add further insulation to your body heat by limiting heat exchange from the background.

Duvet

Although it may surprise you, a duvet is one of the better pieces of equipment for providing insulation while also being quite easy to clean.

When it comes to comfort and insulation, it might as well be a competitor for the sleeping bag itself; however, they are quite heavy to carry, which can reduce their value.

If interested, you can check this article on Can You Use A Duvet For Camping?

Final Thoughts

When it comes to winter camping, a space blanket is probably the most lightweight option, but a bivy camping setup isn’t far behind.

For any survival situation, both are capable of protecting you from sudden weather changes. If you’re just getting started with ultralight hiking, a bivy is a good place to start because of its ease of use and all-around insulation.

However, if you are more accustomed to it, a space blanket as a tarp accompanied by a sleeping bag may be a better option for you.

Anyways, as always, stay safe and happy adventuring!