Emergency Blankets, what is the skinny?

Marion David Poff

Marion David Poff

Joined
Oct 8, 1998
Messages
5,403
So,

Are Emergency Blankets worth carrying?

I am speaking of the mylar coated plastic ones, marketed to save you life.

But I think I saw someone saying that the mylar is not the thing, that the plastic does the work.

What is the story?

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Thank you,
Marion David Poff aka Eye, Cd'A ID, USA mdpoff@hotmail.com

My Talonite Resource Page, nearly exhaustive!!
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"Many are blinded by name and reputation, few see the truth" Lao Tzu
 
For the real story on space blankets you can get Doc Ron's video on making survival kits (a must for anyone contemplating it). But in short it is indeed the mylar that does the trick and reflects the heat either back to you (in cold weather) or away from you (in bright sunshiny hot weather).
We always carry at least three on SAR missions and in my regular day pack. That way if I run into a survivor who needs one I don't deprive myself or if the day hike turns into an "oh crap am I lost" two or three day hike I'm covered (they tear easily). Even torn they can be used to isulate you inside your outer layer of clothing (thanks Doc Ron for that tidbit). At the price (couple of dollars apiece in the Wal-Mart)why not stock up.
Recently I have been looking for the heavier type which had OD green plastic on one side and Mylar on the other. It was more like a real blanket and much more durable. I have been unable to locate them. I think it would make for a good bottom of the day pack support (inside). Sportsman's Guide used to sell them but I haven't seen them advertised recently. Any one know where they have gone?

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Where no law exists there still must be justice- Dan Mahoney
 
I have actually had to use one. Got stuck in a state park and I ended up spending the night (that's another story). My first impression was 'that's a big blanket from such a small package.' I built a small fire and much to my surprise when I woke up, I was pretty warm, even though my fire was long gone. I didn't know the 'put it in your clothing' trick at the time, but it worked fine for me anyway.

They work. As a side note, once you unfold it, forget about folding it back up.



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-Kevin
"Oderint dum metuant"
Riddler, Hoodlum, Bon Vivant.
 
As a side note...

There are five heat loss mechanisms.
Conduction, convection, radiation, respiration and Perspiration/wetness

The things excel at reducing heat loss to convection/advection (wind)
are helpful with heat loss to radiation
and are water tight so rain (wetness is reduced.

They are almost useless against conduction. Lay on the cold ground and you will get cold. Can't do much about respiration
wink.gif


Pieces of it make good improvised sun glasses and they are fantastic for shelters in the desert to keep the hottest sun off your back/neck while you rest through the day.

They are good for signalling.

In my opinion they are well worth the weight however I generally just carry a heavy duty trash bag in my back pocket. It works about the same in cold weather but they last longer and fit in the pocket like a snot rag.

Ron

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Learn Life Extension at:

http://www.survival.com ]
 
Hi Marion,

Campmor sells a "space blanket" that's bigger (about 20%)then normal and printed on it are "survival" instructions, that all for under $6.

All first Aid people in our club carry at least 2 of those tiny packages with them.

They also sell the more permanent version that is reusable many times and has one green or orange side of tuff fibrous plastic and the other side is heat reflecting aluminium colored mylar.
They call that "car picknick blankets" in Holland and I'm planning to get one just to see how good they are.
The only disadvantage is that they weigh about 15-20 times more then the small thin mylar space blanket and are also a lot bigger when folded and so take up a lot more room.

Cheers from Holland,

Bagheera


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Aluminized Mylar was developed for the space program to control heating of spacecraft (particularly lunar landers). Mylar is a comparitively tear-resistant and heat resistant plastic. It is a registered trademark of DuPont for a thin polyester film used in things like recording tape and floppy disks (if memory serves me correctly). In order to make it reflective it is "aluminized", coated with a very thin layer of aluminum (I think by vaporizing the aluminum electrically in a vacuum and letting the aluminum atoms coat the mylar). The aluminized mylar would reflect the intense infrared, visible, and ultraviolet light from the sun outside the shelter of earth's atmosphere. It would also reduce the loss of spacecraft heat when shaded from the sun by reducing infrared light emission from the spacecraft. It is a basic principal of optics that a surface that reflects electromagnetic radiation (light) of a particular wavelength will also be a low emitter of that wavelength. This is one of the reasons that thermos bottles are not only insulated by vacuum, the liners are also aluminized to prevent radiative heat transfer. A more subtle effect as I recall is that a thin metal coating over a dielectric (glass or plastic) is a particularly effective reflector with even a very thin coating of metal. This thin coating also protects the mylar itself from ultraviolet light damage (UV attacks plastics).

As a rescue blanket aluminized mylar has several advantages. The aluminizing will reflect the sun off of you or can be used to reflect visible and infrared light from a fire to where you want it to go. When you wrap yourself in one you will not lose much heat by radiating infrared light out into the sky or into cold terrain. The mylar will also serve as a great wind block. It won't insulate you significantly from direct contact to something cold, but it works great in combination with clothing or a light blanket. Mylar is more tear resistant than the polyethelene of garbage bags, but it is much thinner than a 33 gallon trashcan liner. Both the trash bag and mylar work well for keeping off the wet. I like to carry both. One in my pocket and one in my pack. A plastic bag with a head hole makes a great pancho.

The big disadvantage of plastic coverings is moisture build up (sweat). I tend to get too hot in a space blanket and sweat a lot. I often find them too hot.
 
They sound great, and I personally know of them saving some butts. A group of climbers were climbing the East Face of Mt. Whitney in, I think, 1998. They were not that familiar with the climb, and lost the route early on. After finally finding the route again, they ran out of daylight before completing the climb. They ended up roping themselves into a cliff ledge, and sitting there huddled up all night, with minimal cold weather clothing, at about 12,000 ft. Fortunately, they HAD brought a couple of space blankets with them.

One of those stories with a good ending, that you never hear about.

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iktomi
 
I`ve used on in the field and I was less than thrilled with it. It was better than nothing though FWIW. The weather got colder than expected on night when I was camping in a small leanto shelter. It was in the high 40s with a cold breeze blowing. The shelter was pretty good protection from the wind and I had a small fire going all night but I was nowhere near comfortable or warm. When it stayed on I`d say it was maybe as warm as a flannel sheet. I had a heavy canvas groundcloth and a split trashbag covering about 4" of dry leaves under me and the spaceblanket on top. It wasn`t tooo bad as long as I didn`t let the wind get under it. However they`re so light the slightest breeze seemed to lift it right off me and sucked the heat right out. It also crinkled loudly enought to wake me up several times. I ended up splitting another big trashbag and put that over the spaceblanket. That helped. If I`d had even a light blanket to put over it(or if it hadn`t been windy) I think it would have been much more effective. On the plus side it did help keep the wind off me when it stayed put and it made a good reflector when I wrapped it around me and sat in front of the fire. For the size/weight and price it`s a good thing to have but I wouldn`t count on one unless I had to. FWIW I still keep 2 in my pack. I`ve been meaning to try one of the heavier ones too. Marcus
 
At night, if you point an infrared radiometer at a clear night sky, the temp will be much colder than you might imagine. For instance, during a summer night in the Arizona desert, when the temp was near 30 degrees C, the radiant temperature of the clear sky was -3 degrees C.

When we are exposed to a clear night sky we constantly emit radiant heat towards it and we will receive very little in return because of the huge temperature difference. So the sky tends to act as a radiant "heat sink," basically soaking up our radiant heat. The rate of radiant heat loss is proportional to the temperature difference between the cool night sky and our bodies.

Any barrier you can erect between you and a clear night sky will reduce the rate of radiant heat loss markedly. Thus any space blanket can be remarkably effective when the sky is clear and it could spell the difference between having and not having hypothermia.

One of the reasons we get frost even when the ambient ground temperatures are above freezing is because of radiant heat loss and this is why citrus growers use smudge pots because the smoke makes a barrier between the fruit trees and the clear night sky and reduces radiant heat loss.

You can make ice cubes outdoors when the temperature is above freezing by putting water in a shallow pan and leaving it sit out in the open, exposed to a clear night sky and insulated from the warm earth. Suspending the pan over an open pit can be effective. The air has to be calm, otherwise there is a convective transfer of heat from the wind to the pan of water.



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Hoodoo

The low, hoarse purr of the whirling stone—the light-press’d blade,
Diffusing, dropping, sideways-darting, in tiny showers of gold,
Sparkles from the wheel.

Walt Whitman
 
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