Space blanket : myth or reality

12:17 p.m. on March 6, 2012 (EST)
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I read a book about hypothermia recently : Hypothermia, Frostbite, and Other Cold Injuries: Prevention, Survival, Rescue, and Treatment :

http://www.amazon.ca/Hypothermia-Frostbite-Other-Cold-Injuries/dp/0898868920/ref=sr_1_1?ie=UTF8&qid=1331052755&sr=8-1

One of the author claims that using a good space blanket (it was more a space sleeping bag) can add several degrees to a sleeping bag rating by preventing radiative heat loss. I wanted to put that claim to the test and did it last night.

Here is the experiment setup :

The night temperature ranges from -12.5 to -16.5 celsius (9.5 F to 2.3 F). I decided to use a space blanket inside my sleeping bag.

By experience I know my bag is good down to 14 F without layering too much (I never used expedition weight thermals) and good down to 6 farenheit with a VBL bag.

I started the night with the space blanket inside my sleeping bag, bu i very quickly remove half it, letting only my legs covered by it. even so I was too warm at around 6F (-14.3 celsius). I had to remove the E-blanket as I was starting to sweat quite a lot. I changed for the VBL liner and get some good sleep until around 4 AM. It was -15.1 celsius (5 F) and my right leg and shoulder where painful due to the cold. I knew I was too cold so i changed again for the space blanket. but i just covered my legs. I felt asleep and woke up in the morning. 

conclusion : space blanket add some warmth. More than a mere VBL liner.

Summary

Temp rating with midweight thermals : 14 F

temp rating with midweight thermals and VBL liners : 6 F

temp rating with midweight thermals and Emergency sleeping bag : lower than 2F. 

Remarks:

-my bag is narrow on the bottom but really roomy on top. Radiative heat loss is consequently higher on top. I expect the temp rating gain on the top to be higher but i couldn't put it to the test as I was to warm.

-the gain with the space blanket here is bigger that 12 F (6celsius) wich is remarkable. But I suspect this gain to be less with high loft sleeping bag. Cause heat radiation cannot cross thick layer of insulation.

- My space blanket was the cheapest one I could find.

-I always feel colder at the end of the night when sleeping at the limit of my sleeping bag capability. Which is normal since I suspect i'm not in a steady state condition. I have to produce more heat than normal.

4:16 p.m. on March 6, 2012 (EST)
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The problem with the space blanket is that they don't breathe at all.  It's probably why you sweated.  I think one of the alpine climbers said that they used to use one underneath there pad until they got a pad that had one integrated into it. 

I think that using one like a quilt on your sleeping bag might be a good option as long as you hung your bag out to dry after sleeping in it.

5:54 p.m. on March 6, 2012 (EST)
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Space blankets really work best when close to the skin and not very well after that.

Since very little heat radiates from the outside of a thick sleeping bag, there's not much to reflect back, and most of that will just make it back to the outside layer of the bag.

And while the sweat can be a problem if you're just using one for extra warmth, they are really meant for emergency situations where you're already too cold to sweat very much!

10:15 p.m. on March 7, 2012 (EST)
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That's the purpose of a vapor barrier liner to be non breathable at all. Of course you have to be careful and ventilate the bag properly and you need some experience to use it. 

10:17 p.m. on March 7, 2012 (EST)
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cool report.  thanks.  for some reason, my old job had a box of these, and I grabbed a handful.  I always take one with me, but I've never even opened one.  WHAT WOULD THE ULTRALIGHTERS THINK OF THAT???

10:57 p.m. on March 7, 2012 (EST)
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What about a big space blanket on the outside of the sleeping bag

12:00 a.m. on March 8, 2012 (EST)
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Callahan said:

What about a big space blanket on the outside of the sleeping bag

 The space blanket stops thermal radiation (IR lightwaves). Those wave have long wave length, implying they have some difficulty to cross thick insulative layer. So if you put your space blanket around your sleeping bag you will fill the effect on the bottom of your bag. You may feel some effect on top of the bag as some heat is lost but it is much more efficient if the space blanket is just next to the heat source (you). 

Bottom line : If you put the space blanket on your sleeping pad for example it will be effective. 

12:04 a.m. on March 8, 2012 (EST)
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Zeno Marx said:

cool report.  thanks.  for some reason, my old job had a box of these, and I grabbed a handful.  I always take one with me, but I've never even opened one.  WHAT WOULD THE ULTRALIGHTERS THINK OF THAT???

 For temp above 10F, I don't think a VBL is very practical. Nonetheless it seems that some UL do use space blanket. 

2:13 a.m. on March 8, 2012 (EST)
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Good report Brumo...Yeah, I use a AMK Heatsheets emergency bivvy almost year 'round, for many different purposes. Based on my needs, it's a groundsheet, VBL, or SOL insurance...

12:48 p.m. on March 8, 2012 (EST)
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Space blankets make good fire heat reflectors.

1:09 p.m. on March 8, 2012 (EST)
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I feel the term, "SPACE-Blanket" is a misnomer.   Kinda like NASA, or some-such developed it.

Although; at the moment, I can't think of another name.

If you are in deep space, I don't think one of these will help you.

                                   *

                        pax vobiscum

                              ~ r2 ~

6:56 p.m. on March 8, 2012 (EST)
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I don't remember where/when I had my first experience with them but I know they work very well. I've always called them a survival blanket though I think they do come from a fabric that is/was used to line space suits. For longer than I can remember now, I've had at least one in every pack I own, especially day packs. They never get taken out so they will be there in an emergency. Also have one in each vehicle.

Besides a blanket they can be improvised into a dozen things easily. Collect rain water, Carry water, transpiration bag, distill water vapor from the ground, make a tarp or shelter, a rain poncho, wind screen, reflective signal, etc...

My acupuncurist uses them in her office/practice. When your half naked and stuck full of needles from head to toe, the blanket is so lite, it can lay across the needles and really makes a big difference. She's a miser with the heat...

Like Ocala said, I wouldn't use it inside a sleeping bag, they don't breath AT ALL.

7:13 p.m. on March 8, 2012 (EST)
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Robert

Space blankets are what they wrap satellites with to keep them insulated from solar radiation.

8:39 p.m. on March 8, 2012 (EST)
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Funny thing is that it was indeed developed by NASA (1964) to be used in space as explained above...

7:15 a.m. on March 9, 2012 (EST)
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  I've been called a "space cadet".   I reckon I'll need to shlepp one of these blankets.

I have a couple somewhere (?).   Never used 'em.

Probably good for keeping the sun from baking my Vanagon's dashboard, in the Summer.

                            pax vobiscum

                                 ~ r2 ~

8:22 a.m. on March 9, 2012 (EST)
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Wonder if I could figure out how to laminate it to the roof of my car. 

4:23 p.m. on March 9, 2012 (EST)
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peter1955 said:

Space blankets really work best when close to the skin and not very well after that.

Since very little heat radiates from the outside of a thick sleeping bag, there's not much to reflect back, and most of that will just make it back to the outside layer of the bag.

And while the sweat can be a problem if you're just using one for extra warmth, they are really meant for emergency situations where you're already too cold to sweat very much!

I am going to disagree with all three of these observations.

Oriented properly, a space blanket will reflect heat several feet.  I have used one to wrap my bag, and once used one to reflect heat from a camp fire.  In both applications the effect was significant, albeit as a bag wrap the warmth may have been the result of the blanket's VBL qualities.

As for heat radiating from the outside of a sleeping bag, the same amount radiates from a summer bag as a polar bag; otherwise the polar bag would retain over time until it was hot enough to bake you.  The difference between bags is a high R factor means it takes longer for heat to radiate through to the outside of a polar bag.  But once both bags have “warmed up” they will radiate heat with equal speed.

Lastly, if you are in an emergency and cold, any amount of sweat reduces the effectiveness of your warming technology, unless used in conjunction with VBL.

Ed  

12:02 a.m. on March 10, 2012 (EST)
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Robert Rowe said:

I feel the term, "SPACE-Blanket" is a misnomer.   Kinda like NASA, or some-such developed it.

Although; at the moment, I can't think of another name.

If you are in deep space, I don't think one of these will help you.

                                   *

                        pax vobiscum

                              ~ r2 ~

 RR, NASA developed the space blanket in 1964.

5:11 a.m. on March 10, 2012 (EST)
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I am now learning that.

Should have 'Googled it', as most here probably have.

Very few would have remembered, otherwise.

Hope your memory is that good.

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                      pax vobiscum

                             ~ r2 ~

10:32 a.m. on March 10, 2012 (EST)
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Robert Rowe said:

I am now learning that.

Should have 'Googled it', as most here probably have.

Very few would have remembered, otherwise.

Hope your memory is that good.

                                 *

                   

                      pax vobiscum

                             ~ r2 ~

 Sorry, but growing up during the fun times of NASA, the fact never left my mind. sorta like TANG and SPACE FOOD STICKS.

11:31 a.m. on March 10, 2012 (EST)
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Space Blanket - A vacuous partner that keeps you warm at night.

Ed

1:58 p.m. on March 10, 2012 (EST)
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Giftogab, if, in your upcoming journey you have an opportunity to sample mango flavored Tang, jump on it. I tried it a few years back when I found it at an outlet store. The container was labeled in arabic for the middle eastern market. I understand it is now being exported to India and associated geographical areas.

3:49 p.m. on March 10, 2012 (EST)
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As it happens, I did Googled the info on the space blanket but only because I already knew that there was a connection with NASA. Google told me exactly what that was. There are many products that are falsely claimed to have been developed for or by NASA, for example Tang. Tang was concocted in 1957 and marketed commercially  in 1959 , 2 years before being used on a space flight. Franco

11:35 a.m. on March 11, 2012 (EDT)
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Space blanket--Crinkle crinkle crinkle noisy noisy noisy. 

Here's my space blanket story--many years ago when I was a Boy Scout I took the Wilderness Survival class.  One of the requirements was to spend a night out in the woods with a minimum amount of gear.  Since it was Scout Camp we went as a group to the designated area.  I had my coat for insulation and that was about it.  Another kid had a space blanket and offered to trade me his space blanket for my coat (just for the night).  "Wow," I thought, "a space blanket.  Just like the astronauts.  I'll trade!"  Long story short I didn't freeze to death, but I think I should have kept my coat. 

Ahh, the ignorance of youth.

3:12 p.m. on March 12, 2012 (EDT)
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whomeworry said:

peter1955 said:

Space blankets really work best when close to the skin and not very well after that.

Since very little heat radiates from the outside of a thick sleeping bag, there's not much to reflect back, and most of that will just make it back to the outside layer of the bag.

As for heat radiating from the outside of a sleeping bag, the same amount radiates from a summer bag as a polar bag; otherwise the polar bag would retain over time until it was hot enough to bake you.  The difference between bags is a high R factor means it takes longer for heat to radiate through to the outside of a polar bag.  But once both bags have “warmed up” they will radiate heat with equal speed.

 This is physically totally incorrect. I don't have time to explain it today. But next time I'm going to elaborate on that.

8:55 p.m. on March 12, 2012 (EDT)
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Brumo said:

whomeworry said:

As for heat radiating from the outside of a sleeping bag, the same amount radiates from a summer bag as a polar bag... ..once both bags have “warmed up” they will radiate heat with equal speed.

 This is physically totally incorrect...

I may not be eloquent in describing the physics, but my prior statement is generally true.  If you continue to pump heat into a mass it will get hotter until the heat radiated equals the heat input, or the retained heat increases until it destroys the object.  This is true regardless the warmth (R factor) of the mass.  Thus over time a summer bag and winter bag will reach their warmest respective potentials for its occupant, at which point both bags will be radiating heat at the same amount and speed as emitted by its occupant.

Ed

9:39 p.m. on March 12, 2012 (EDT)
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Brumo said:

 This is physically totally incorrect. I don't have time to explain it today. But next time I'm going to elaborate on that.

 To understand what's happening it's good to proceed by analogy. Thermal radiation is a kind of light. It's just infrared light. It is produce by heat or warm sources. Here are some examples :

  • fire, it can be freezing cold outside but you'll fill the heat of the fire. The heat you feel is not only the air that's warmed by the fire but also thermal radiation.
  • Sun : same thing as before. There's a huge difference between a sunny day at-20 and night at the same temp. Again radiation heats you.
  • yourself or any animals.

Now radiation does depend on the thickness of the insulation. If you put a light bulb (flash light or head lamp) inside a summer sleeping bag you will see the light  through it.  This is not the case with an expedition sleeping bag. With thermal radiation it is exactly the same thing. Well you can say but thermal radiation has a different wave length. But think about this one : If the radiation that goes trhough the sleeping bag doesn't depend on the thickness of the insulation it means that your sleeping bag act like a window (glass) but for infrared light, i.e. the infra red light is transmitted accross the sleeping bag. But most material are opaque. So it is highly improbable that down, primaloft and all other insulator used in sleeping bags are perfect infra red transmitter. And in fact it is not.

So what is happening. There is 3 way thermal radiation can interact with matter. it is either transmitted, but we already exclude that, either absorbed or reflected.

Let's first talk about absorption (this is also an answer to the argument of infinite heating mentionned by whomeworry) : It is true that radiative heat will heat the inside of the sleeping bag. The light will be absorbed by matter. This means that photon (light particle) are absorbed by the insulator molecules. Let say that the insulator is down. The down molecules will recoil and vibrate. This phenomenon is precisely the heating processed whomeworry talked about. But very few photon are aborbed by the molecules that are far away from the body. On the contrary molecules that are close to the heat source will become a heat source and radiate but in all direction some will go back to the body and some photon will radiate to the outside (if it's hard to follow draw a pictures). If the surrounding is really cold But even if all the photon were radiating to the outside, the surrounding maybe very cold. Meaning that the flakes far away from your body and close to the surrounding need much more photon to be heat up than the one close to your body. The are continuously cool down by the surrounding and so don't radiate as much as the flakes next to skin. And the closer they are from a closer surrounding the less they radiate. Moreover the flakes in contact with each other will evacuate heat by conduction.

The error you committed whomeworry is that yoy consider your system to be an isolated system. But it's not. At first approximation the thermodynamical system here is a thermostat, the surrounding is at constant temperature no matter what, the heat you furnish to your surrounding is negligeable. It is not quite true if you use a bivy bag or any kind of shelter, But outside your shelter it is a true thermostat (at least at night).

Let's now talk about reflexion : The thermal radiation can be reflected completely to you. You made a (false) statement about the fact that the retained heat will ultimately destroy yourself. Suppose you use a space blanket next to skin. All the thermal radiation is reflected back to you. All of it. But you don't start to cook up. Why?? Because thermal radiation is not the only way to loose heat. There is convection, evaporation, conduction. The heat reflected back to you will heat the molecules of your skin. But your body like to be at 98 F. So if the temp goes above that, it will start to sweat (but this doesn't count cause the warm vapor will stay inside the blanket), your breathe will evacuate a lot of heat to, the ground will evacuate some heat, the space blanlet will evacuate some heat by conduction, the air oustide the space blanket can evacuate heat by convection and of course you can ventilate your bag. 

The space blanket is definitely more effective when used next to skin. If you use it to wrap your sleeping bag it will still have some effectiveness. First the outer shell of your sleeping bag radiates a little bit (as it is not at the same themp as the surrounding. Second it will reduce the air flow, air flow even as low as few 1 foot per second, can act add a non negligeable wind chill, specially near the zipper (FYI : This had been tested in labs). So even if your sleeping bag has a totally windblock shell the thin warmer air layer just next to the outer shell maybe swept out by a very feeble air flow.

My opinion (here it is an opinion) but I may be wrong, is that a space blanket used to wrap your sleeping bag has no more effectiveness than a bivy bag + a space blanket underneath your sleeping bag. 

 

9:47 p.m. on March 12, 2012 (EDT)
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whomeworry said:

Brumo said:

whomeworry said:

As for heat radiating from the outside of a sleeping bag, the same amount radiates from a summer bag as a polar bag... ..once both bags have “warmed up” they will radiate heat with equal speed.

 This is physically totally incorrect...

I may not be eloquent in describing the physics, but my prior statement is generally true.  If you continue to pump heat into a mass it will get hotter until the heat radiated equals the heat input, or the retained heat increases until it destroys the object.  This is true regardless the warmth (R factor) of the mass.  Thus over time a summer bag and winter bag will reach their warmest respective potentials for its occupant, at which point both bags will be radiating heat at the same amount and speed as emitted by its occupant.

Ed

 This is because you're confusing heat with thermal radiation. The point here is the net heat balance. Thermal radiation is just one component of it. The heat is lost by conduction, convection, evaporation and radiation. I can also elaborate on that but I think every body is already sleeping after my previous explanation.

5:32 p.m. on March 13, 2012 (EDT)
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Brumo said:

This is because you're confusing heat with thermal radiation. The point here is the net heat balance...

Sorry if the verbiage chosen was misleading.  I was trying to make a very simple, relatively non-technical statement, and not obscure the concept with the nuances of thermodynamics.  I wanted to make a very simple point: At some point the amount of heat leaving the bag by whatever the mechanism, - radiation, convection, etc - will equal the amount of heat emitted by the occupant, something you describe as net heat balance.  This is true regardless the bag is a summer bag or an artic bag.  

Ed

6:40 p.m. on March 13, 2012 (EDT)
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whomeworry said:

Brumo said:

This is because you're confusing heat with thermal radiation. The point here is the net heat balance...

Sorry if the verbiage chosen was misleading.  I was trying to make a very simple, relatively non-technical statement, and not obscure the concept with the nuances of thermodynamics.  I wanted to make a very simple point: At some point the amount of heat leaving the bag by whatever the mechanism, - radiation, convection, etc - will equal the amount of heat emitted by the occupant, something you describe as net heat balance.  This is true regardless the bag is a summer bag or an artic bag.  

Ed

 This is true, this is the conservation of energy. But what you said was misleading since we were talking about thermal radiation. 

6:42 p.m. on March 13, 2012 (EDT)
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whomeworry said:

As for heat radiating from the outside of a sleeping bag, the same amount radiates from a summer bag as a polar bag; otherwise the polar bag would retain over time until it was hot enough to bake you.  The difference between bags is a high R factor means it takes longer for heat to radiate through to the outside of a polar bag.  But once both bags have “warmed up” they will radiate heat with equal speed.

...

Ed  

 Here you talked about the radiation. 

8:57 p.m. on March 13, 2012 (EDT)
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Brumo said:

 Here you talked about the radiation. 

Yes, as mentyioned earlier I misapplied a term, lacking a better one in my mind at the time to simply describe all manner of heat loss through the bag.  Hopefully anyone interested has been able to understnd the jist of this point, helped along by your clarifications.

Ed

10:35 p.m. on March 13, 2012 (EDT)
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whomeworry said:

Brumo said:

 Here you talked about the radiation. 

Yes, as mentyioned earlier I misapplied a term, lacking a better one in my mind at the time to simply describe all manner of heat loss through the bag.  Hopefully anyone interested has been able to understnd the jist of this point, helped along by your clarifications.

Ed

 

Anyway, It seems that the main point where we seems to disagree is that the space blanket is more effective when worn next to skin and less effective (at least for radiation) when you wrap your bag with it.

3:11 a.m. on March 16, 2012 (EDT)
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I use the space blanket to cover my dog so he stays warm in the tent on extra cold nights (he has pretty short fur).

4:20 a.m. on May 13, 2012 (EDT)
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I was wondering if you could put a space blanket on top of hammock netting that had a tent over it and it would still keep you warm? Aparently the fact that they don't breathe well this air gap would help. Also ,I saw a few videos of reflecting heat from these off of fires, why not body heat inside a hammock tent .In the one I'm talking about there wouuld be about 8 inches from your face .?????? Any experience here???

7:34 a.m. on May 13, 2012 (EDT)
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Tam, generally speaking in a hammock we are more concerned with heat loss from below more so than on top. I know of several in the hammock community that use a space blanket in conjuction with or as a replacement for a sleeping pad.

It is not advised to put a space blanket over the hammock ridgeline, as you will wake up in a rain shower of condensation lol. Those of us who use 'hammock socks' which is esentially a piece of fabric that completely encloses a hammock to make a dead air space make them out of a DWR coated breathable fabric, such as momentum.

So in short, you would be better off sleeping on top of the space blanket vice putting it over you. Even in this case your back would be a little damp when you wake up, but thats better than your sleeping bag being damp.

A good alternative is to use a cheap car sun shade. Like the 1$ ones from the dollar store. They are esentially a space blanket/foil coated piece of 1/8in foam. I have used these sun shades by them selves down to about 45-50F or so. They also work great adding them into other sleep systems, then add about 10-15F or so i would guess, the same as a space blanket but more comfy and don't make all the crinkling noise.

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