How do emergency blankets work?

A woman on the beach wearing an emergency blanket
How do emergency blankets work? We explain the extraterrestrial origins of this piece of safety kit and how to make yours more effective (Image credit: Plume Creative)

If you’re a responsible hiker – and hopefully you are – won’t leave the house without a good first aid kit packed full of items like a bothy bag and an emergency blanket to help you survive an unplanned night in the wild. But unless you know what these items are for and how to use them, they’re basically just adding weight to your backpack and slowing you down. In this article, we explain how emergency blankets work and how to use them in a worst case mountain scenario. 

What is an emergency blanket? 

A folded emergency blanket

An emergency blanket – also known as a space blanket, survival blanket or first aid blanket – is an ultra lightweight and extremely packable metallic blanket (Image credit: Michael Burrell)

An emergency blanket – also known as a space blanket, survival blanket or first aid blanket – is an ultra lightweight and extremely packable metallic blanket made from heat reflective plastic sheeting called Mylar. Usually one side of the blanket is brightly colored so that rescuers can spot you, and the other side is aluminium, but sometimes both sides are aluminium. An emergency blanket basically looks a lot like a large, flimsy sheet of aluminium foil and is used by athletes, mountaineers, medics and even astronauts to keep warm in extreme situations. 

The technology used in emergency blankets was developed by the space program in the 1960s as a means to deflect the sun’s heat and protect spacecraft, equipment and personnel from the heat of the sun. The technology works by using a technique called vacuum metallization which had previously been reserved for mirror making and manufacturing novelty items like tinsel. Metallizing involves applying a metal coating onto a non-metal surface – in this case, a thin layer of aluminium to plastic. The shiny aluminium coating deflects infrared rays, which are invisible rays that we experience as the sensation of heat.

Today, emergency blankets are staple items in hiking first aid kits and at the end of marathons and are used by mountain rescue and even in large scale disaster relief efforts.

How do emergency blankets work? 

Three women wearing emergency blankets after a race

The reflective coating on an emergency blanket reflects your own body heat back towards you to keep you warm (Image credit: SolStock)

So if this technology is designed to deflect heat, how does it help you when you’re stranded on a mountain in freezing temperatures? The clever engineers at Nasa might have developed the material used in emergency blankets as a means to keep heat out and stop their precious equipment from being destroyed in space, but they quickly realized that they could also use the technology to keep heat in, simply by turning it around.

If you find yourself in an emergency situation where you’re losing body heat faster than you can generate it – say you’re lost on a long hike, fall through ice or have just completed a very long and gruelling trail run – you’re in danger of developing hypothermia. If you can’t get indoors immediately, you can whip out your emergency blanket from your first aid kit and wrap it around yourself to conserve and increase your own body heat. Instead of turning the foil side towards the sun to keep heat out, you turn it towards your own body where it reflects your body heat back towards you. 

Conversely, if you find yourself lost without shade on a very hot hike, you can use your emergency blanket to reflect the sun’s heat off you, by turning the foil side out.

How effective are emergency blankets? 

A folded emergency blanket

According to Nasa, emergency blankets reflect up to 90% of your body heat (Image credit: Liudmyla Liudmyla)

According to Nasa (opens in new tab), emergency blankets reflect up to 90% of your body heat, which sounds pretty effective indeed, and they are waterproof and windproof, which adds a lot of value in a pinch. However, there are some issues with emergency blankets that can reduce their effectiveness. 

First, they come in different sizes and you need to make sure that yours is big enough to fully cover your body. Next, though they do come in bivy-style designs these days, your basic emergency blanket usually comes in a simple blanket form. This means that they don’t have zips to seal out the cold. You can wrap yourself up in it like a burrito to help, but it won’t seal out as much cold as an item like a sleeping bag. Finally, they’re not particularly robust –  they have a short shelf life and degrade easily, meaning if you’ve been carrying yours around for a few years and then disaster strikes, it may not be as effective as you hoped. 

If it’s all you have, an emergency blanket will provide you with some warmth until you can get to safety, but for prolonged exposure, it’s actually most effective when combined with other emergency gear. For example, you can use it to line your emergency bivy sack or best sleeping bag, or place it underneath you, foil side up, to act as a groundsheet while you’re huddling inside your bivy or bothy bag. You can also use yours to make an emergency shelter if what you really need is to keep moisture at bay.

Can you sleep with an emergency blanket? 

A man sleeping in a bivy sack with snowy mountains in the background

In an emergency situation, if it’s all you have, you should roll yourself up in your emergency blanket to sleep, but it won’t provide much comfort (Image credit: Galen Rowell)

In an emergency situation, if it’s all you have, you should roll yourself up in your emergency blanket to sleep, but it won’t provide much comfort as it’s not insulated or padded so it’s definitely not an appropriate substitute for a sleeping bag and sleeping pad. That said, for the very low cost and small pack size, it’s still worth carrying in your first aid kit for when push comes to shove. For more information on what to do in an emergency situation, you’ll want to read our article on how to build a natural shelter

Julia Clarke

Julia Clarke is a staff writer for and the author of the book Restorative Yoga for Beginners. She loves to explore mountains on foot, bike, skis and belay and then recover on the the yoga mat. Julia graduated with a degree in journalism in 2004 and spent eight years working as a radio presenter in Kansas City, Vermont, Boston and New York City before discovering the joys of the Rocky Mountains. She then detoured west to Colorado and enjoyed 11 years teaching yoga in Vail before returning to her hometown of Glasgow, Scotland in 2020 to focus on family and writing.