How Space Blankets Work

How can something so thin keep you warm? Even though it sounds cliché, it's space age technology.

Manufacturers created the material by depositing vaporized aluminum onto a very thin plastic film. The resulting material is thin, flexible and thermal-reflective -- meaning it reflects heat. The aluminum helps redirect infrared energy, which is just a fancy word for heat. Depending on how the blanket is made, it can reflect heat away (that's how NASA used it to cool down Skylab), or it can reflect heat in (that's how it regulates body temperature). Sometimes called a passive warming system, space blankets assist the body in conserving that infrared energy.

Let's focus on how space blankets work to keep a person warm. First, we need to understand how a body loses heat in the first place. Excessive heat loss leads to hypothermia, an extremely dangerous condition. Space blankets stop both evaporative and convective heat loss.

Evaporation is the process of water changing from a liquid to a gas. In the case of a person, the liquid can be sweat or wet clothing. Evaporation uses a lot of energy and lowers the body temperature. This is why you need to be careful not to get too sweaty in cold weather. Your body temperature will drop quickly once you stop exerting yourself -- and the evaporation of sweat will make you even colder. To prevent evaporative heat loss, you should try to stay as dry as possible. A space blanket helps slow down the process of evaporative heat loss by increasing the humidity of the air next to the skin.

Convection is a lot like conduction. Conduction is the transfer of heat or cold between two objects. For example, if you sit down on a pile of snow, your backside will get colder, and the snow will get warmer. With convective heat loss, however, the cold object is moving -- like a cold wind. The wind takes the warmth away from whatever it touches. The faster the object is traveling, the colder you'll get. You can help reduce convective heat loss by wearing layers of clothing as insulation. A space blanket forms a barrier between the wearer and the wind, providing insulation.

Lastly, we also lose body heat through radiation -- it simply radiates off our body. The reflective agent on space blankets -- usually silver or gold -- reflects about 80 percent of our body heat back to us.

Next up, we'll talk about the many ways you can use a space blanket for survival.

An important part of any first aid kit, a space blanket provides you with more benefits than just keeping warm. However, keeping warm should always be your first priority in any type of survival or adventure situation.

Some of the most useful things about space blankets are that they're lightweight, take up very little space and don't cost very much. A typical space blanket costs less than $4 and weighs about 3 ounces (85 grams). Folded up, it's about the size of a deck of cards, and unfolded it's about 56 by 84 inches (142 by 213 centimeters) [source: REI].

Here are just a few ways you can utilize a space blanket in a survival situation:

Emergency blanket -- Of course, the space blanket's main purpose is helping you or someone else stay warm. It's especially useful in a first-aid kit if someone is going into shock. Wrap the blanket around the person, tucking it in on the sides and under the feet in order to keep body heat in and cold out. Cover the person's head with a hat or scarf to prevent further heat loss.

Emergency shelter -- In a pinch, you can use your space blanket as a tent, tarp or lean-to. The material is waterproof so it will protect you from rain or wet snow. If you are in a cold weather situation, take advantage of the shiny side of the blanket to reflect heat from a campfire back to you. The metallic surface will bounce the heat of the fire toward you and help keep you warm.

Keep warm -- Besides using a space blanket as a blanket, you can also use it to insulate your space. For example, let's say you become trapped in your car during a freak winter blizzard. Cover the windows of the car with the space blanket -- shiny side in. It will help reflect your body heat back inside the car.

Keep cool -- In the same way that the space blanket reflects heat back toward you, it can also reflect heat away from you. If you're in a tent, and the sun is bearing down on you, put the blanket shiny-side-up on top of the tent. Have you ever seen shiny sun shields on the windows of cars during the summer? Same idea -- the metallic surface of the sun shield reflects the heat of the sun out of the car.

Signal for help -- Because the surface of the blanket is so shiny, it makes a good distress signal. The reflective surface makes it more easily visible from the sky. Some space blankets even come with the letters "SOS" printed right on the blanket itself.

With a little creativity, you can probably find even more ways to use your space blanket.

Space blankets come in different brands, sizes and shapes. Keep reading to find out more.

You can find several different types and brands of space blankets for sale. Find out what kind will best suit your needs.

The traditional space blanket is just a metallic sheet. It folds up into a very small package. It's usually shiny on one side and colored on the other. Some space blankets are bright orange on the colored side for easy visibility in the woods.

The space blankets you see at marathons usually come in a roll or are shipped flat in boxes. Marathon sponsors realized almost immediately that they could advertise their brands right on the sheets -- an inexpensive way to create walking billboards.

Sporting goods stores offer a wide range of space blankets. You can buy a cheap emergency blanket for around $6 -- making them virtually disposable. You can buy more heavy weight, reusable blankets for around $14. You can buy a survival blanket big enough for two people.

Or, if you know you'll be in extreme conditions, you could purchase a bivy sack. A bivy sack (sometimes spelled "bivvy") is short for "bivouac sack." The word "bivouac" means a temporary encampment or casual shelter. Experts recommend bivy sacks for people who need to carry the least amount of weight possible -- campers, mountain bikers, climbers and the like. Bivy sacks are waterproof and shaped like a sleeping bag. You put them over your sleeping bag or -- in warmer conditions or survival emergencies -- use the bivy sack as the sleeping bag itself.

Many bivy sack manufacturers use space blanket technology to make the bivy sack even more valuable. The metallic reflective coating blends with a heavier, stronger material. That makes it waterproof, more durable and less prone to rips and tears. It is a bit heavier than a regular Mylar-style space blanket, but has its own advantages as well.

Here's an example of using a bivy sack in an extreme survival situation: If someone's clothes are soaked and they are in danger of hypothermia, you can remove the person's wet clothes and place him or her in the bivy sack. This way the victim's body won't waste energy trying to warm up cold, wet clothing.

An emergency bivy sack comes folded in a pouch no bigger than the size of a large can of soup and weighs about 6.5 ounces (184 grams). A bivy sack will run anywhere from around $16 all the way up to around $40 or more. It all depends on the quality of the particular item.

To find out more about space blankets and survival gear, check out the links on the next page.