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#125859 - 12/26/09 11:26 AM aluminium heat reflection
chris angus Offline
newbie

Registered: 12/25/09
Posts: 4
Loc: england
Hi everybody i am new to the backpacking light scene so please excuse me if the question i have for you more experienced hikers has an obvious answer that i have missed.I recently bought a cheap thin aluminium blanket thinking that if it does reflect body heat as the makers claim then if i put it on top of my sleep mat i will keep a lot warmer in my bagfor very little extra weight.If this turns out to be the case then my question is this---Why arent jackets lined with aluminium? depending on the thickness of the aluminium cloth used this could possibly do away with the need for fleeces or other mid layers completely.Thereby saving a lot of weight and space in rucksac.Anyway happy trekking to you all in the coming year.

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#125863 - 12/26/09 01:33 PM Re: aluminium heat reflection [Re: chris angus]
oldranger Offline
member

Registered: 02/23/07
Posts: 1735
Loc: California (southern)
My understanding is that the aluminized mylar blankets do indeed reflect radiant heat. Unfortunately, you lose most of your heat through conduction and convection where wool and fleece are more effective. If you are in a vacuum (i.e., space) radiant heat lose is far more significant.

Those blankets are oversold. They do keep the wind and rain out, and they have a place in a survival pack for help in concocting a survival style hideyhole, although there are better products for that nowadays (Heetsheets) IMHO.

I use mine for tent footprints. Very lightweight and effective, although a bit fragile.

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#125865 - 12/26/09 02:15 PM Re: aluminium heat reflection [Re: chris angus]
DJ2 Offline
member

Registered: 01/06/02
Posts: 1347
Loc: Seattle, WA
I have found them useful if you are sitting around a fire on a cold day. If I wrap the blanket around my head and shoulders and leave it open to the fire the blanket will reflect some of the heat onto me.

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#125871 - 12/26/09 04:10 PM Re: aluminium heat reflection [Re: chris angus]
lori Offline
member

Registered: 01/22/08
Posts: 2801
Mylar blankets are:

  • a vapor barrier, making it uncomfortable and sweaty in temps upward of freezing
  • not durable, as in, the really cheap ones are essentially single use items
  • not a comfortable kind of warm - at least, not in the same way a nice sleeping bag can be.


However, it still has a place in an emergency kit, as you can use them if you come upon an injured hiker who's taking a chill in the middle of the day - they can also save your hide if you're caught out overnight without a full backpack. The Adventure Medical bivy with thermolite (around thirty bucks) will be more durable and probably more comfortable, and tends to be what members of our SAR team carry for the victim.

The NeoAir sleeping pad/inflatable mattress actually makes use of the reflective mylar in its baffles to keep the mattress compact and still effective. But it is not comfortable much below freezing unless you add a foam pad to it. Which is to say there are definite limits to a reflective warm layer. Hammock users sometimes use bubblewrap covered with reflective foil - Reflectix is also a home insulation and is additionally used to make heat-retaining cozies for backpacker's pots or dishes or freezer bags - but again, it doesn't keep you as warm as more traditional insulations.
_________________________
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

http://hikeandbackpack.com

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#125875 - 12/26/09 04:44 PM Re: aluminium heat reflection [Re: chris angus]
Jimshaw Offline
member

Registered: 10/22/03
Posts: 3938
Loc: Bend, Oregon
Chris
a long long time ago and far far away my girl friend and I were sharing an old flannel lined sleeping bag in a redwood forest along the coast in California (in fact is was on our second date) smile and it got down to near freezing. Since I was worried about dampness in a redwood forest and it would be cold, I bought and brought one of those space emergency blankets. I wrapped it around us and we slept warmly, but in the morning the top of the sleeping bag was soaked from condensation from our perspiration that condensed against the metalized blanket, it would have just blown away without the space blanket. So any way I tossed it the dumpster as a stupid idea and I have never since carried one. I have to laugh at people who carry them thinking they will help. Maybe if you are a satellite in space it might have some positive effect, satellites don't perspire.
Jim crazy
_________________________
These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.

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#125893 - 12/26/09 09:27 PM Re: aluminium heat reflection [Re: chris angus]
Eugene Offline
member

Registered: 12/26/09
Posts: 60
Loc: San Diego, CA
To answer your question, I think there is a jacket that uses a reflective layer, it's an electric motorcycle jacket. I can't remember which one though since I really don't have a need for those down in San Diego....my perforated leather jacket works fine unless I ride the mountains in the winter.

Thanks for bringing up this topic. I was planning on making a vapor barrier for my sleeping bag. Now I'm thinking I'll make it out of this stuff. This stuff is cheap too.
_________________________
www.eugeneleafty.com

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#125898 - 12/26/09 11:04 PM Re: aluminium heat reflection [Re: Eugene]
lori Offline
member

Registered: 01/22/08
Posts: 2801
Originally Posted By Eugene


Thanks for bringing up this topic. I was planning on making a vapor barrier for my sleeping bag. Now I'm thinking I'll make it out of this stuff. This stuff is cheap too.


Are you going out in subzero temps? A vapor barrier would be miserable for me, I hate being wet when I sleep.
_________________________
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

http://hikeandbackpack.com

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#125899 - 12/27/09 12:04 AM Re: aluminium heat reflection [Re: lori]
Eugene Offline
member

Registered: 12/26/09
Posts: 60
Loc: San Diego, CA
Yeah, there's a good chance of subzero temps. I'll probably hate it at first too, but it can't be worse for getting sleep than the first time I camped in a hammock....the first night I was laughing for hours from swaying, or swaying because I was laughing...
_________________________
www.eugeneleafty.com

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#125902 - 12/27/09 01:13 AM Re: aluminium heat reflection [Re: Eugene]
Jimshaw Offline
member

Registered: 10/22/03
Posts: 3938
Loc: Bend, Oregon
Eugene
Are you aware that vapor barrier clothes fit snugly with the idea that they will prevent perspiration because the air next the skin is already at 100% humidity? If you are in a loose non-breathable bag you will still perspire, only it will condense and run down the liner and soak you and whatever you are wearing in your own sweat. Be prepared to get out of your bag in about an hour and removing the wet liner and getting back into your bag wearing wet sleeping garments. You will then probably be colder than if you hadn't tried the liner. I'm just suggesting that you take a spare set of long underwear and maybe putting your jacket over you and maybe trying it some place safer than several miles from your vehicle for the first try. YMMV
Jim
_________________________
These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.

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#125904 - 12/27/09 03:00 AM Re: aluminium heat reflection [Re: Jimshaw]
Eugene Offline
member

Registered: 12/26/09
Posts: 60
Loc: San Diego, CA
The whole point of a VBL is so that it doesn't breathe. If I was going to quit just because I got sweaty, I wouldn't be considering using a VBL at all. My biggest concern is to make sure any sweat doesn't somehow find its way into my sleeping bag, but as long as I tweak my venting and/or layering correctly, that won't be a problem. Besides, even if the VBL turns into a disaster, the rest of my sleeping arrangement will be able to handle all but the worst of storms. I'm aiming at being comfortable in conditions below -40F for several consecutive days--basically, blizzard conditions. Well, as comfortable as one can be anyway....I still need to arrange how I'll breathe and hydrate so I can stay in the sack all night and not ice up the area around my head.
_________________________
www.eugeneleafty.com

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#125908 - 12/27/09 06:55 AM Re: aluminium heat reflection [Re: chris angus]
Roocketman Offline
member

Registered: 03/10/07
Posts: 203
Perhaps you could consider the counter story to your hypothesis.

If virtuallynobody is using the reflective aluminized mylar "space blanket" in clothing, then why is it that the "space blanket" is so heavily promoted as a way of keeping warm by "reflecting body heat back to your body"?

Maybe it is a matter of a little truth blown out of proportion.

It appeals to those who haven't bothered to read very much about the theory of keeping warm ...

I know that the kind of people who sell magnets for healing most of the ailments of the human body also sell "heat reflecting" products to further cure the ailments of the human body.

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#125916 - 12/27/09 11:33 AM Re: aluminium heat reflection [Re: Eugene]
lori Offline
member

Registered: 01/22/08
Posts: 2801
If those are your temps, I'd use something other than mylar. Too flimsy. Not what you want to bank your life on. Have you looked at vapor barriers like Warmlite?
_________________________
"In the beginner's mind there are many possibilities. In the expert's mind there are few." Shunryu Suzuki

http://hikeandbackpack.com

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#125920 - 12/27/09 02:57 PM Re: aluminium heat reflection [Re: lori]
Eugene Offline
member

Registered: 12/26/09
Posts: 60
Loc: San Diego, CA
What's wrong with flimsy? Do you think that would make it too hard to use, or that it wouldn't be durable? I primarily want it to resist ripping and facilitate a zipper. Thick mylar is available too.

I'm not dead set on a bag either because that adds weight. I'm already planning on having vapor barrier clothing, so I may reuse that to save weight. I briefly looked at Warmlite before, but I'm leaning towards using a rainsuit from Walmart or online motorcycle shop.


Edited by Eugene (12/27/09 02:58 PM)
_________________________
www.eugeneleafty.com

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#125934 - 12/27/09 07:17 PM Re: aluminium heat reflection [Re: Eugene]
Jimshaw Offline
member

Registered: 10/22/03
Posts: 3938
Loc: Bend, Oregon
Eugene
we're just saying try it before you are in a tough spot, maybe try it in your living room.
Peace
Jim
_________________________
These are my own opinions based on wisdom earned through many wrong decisions. Your mileage may vary.

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#125936 - 12/27/09 08:28 PM Re: aluminium heat reflection [Re: Eugene]
Tango61 Offline
member

Registered: 12/27/05
Posts: 931
Loc: East Texas Piney Woods

Dear Mr. Eugene,
Instead of us playing twenty questions and yapping back and forth about mylar, why don't you tell us where you plan on going and what you plan on doing where it is -40F, since you list your location as San Diego.

There are a couple of folks here that have experience in those temps (Alberta and Newfoundland) and can tell you what works and what doesn't.

Also, visit the winter camping section and look at those posts. There is one by TomD that lists another forum that is strictly dedicated to cold weather camping.

Tango61
_________________________
If you think you can, you can. If you think you can't, you can't. Either way, you're right.

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#125986 - 12/28/09 08:52 PM Re: aluminium heat reflection [Re: Tango61]
Eugene Offline
member

Registered: 12/26/09
Posts: 60
Loc: San Diego, CA
Slightly off topic, but I found a bivy that used to have a reflective coating. It'd be interesting to find out why they got rid of it. I imagine it's because the coating was rubbing off and making shiny sleeping bags.
http://www.titaniumgoat.com/Bivy.html

@Tango
I'll gladly share when my plans firm up more.
_________________________
www.eugeneleafty.com

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#126118 - 12/30/09 09:47 PM Re: aluminium heat reflection [Re: chris angus]
Paul Offline
member

Registered: 09/30/02
Posts: 778
Loc: California
aluminized mylar will reflect radiant heat back to your body, BUT - it only reflects radiant heat; (not your biggest form of heat loss); it works poorly at even that unless at an optimum distance for your body - which as I understand it is something like 1/2-3/4" of an inch. Further or closer it loses efficiency pretty quickly. So on the ouside of a sleeping bag (unless it is a damn thin one) it will do very little. On the inside of a sleeping bag, it will do little unless it is performing as a vapor barrier (as others have pointed out). On top of your foam pad, where your sleeping bag is compressed to almost nothing, it will not do much.
In an emergency, where you use it on the outside of your clothing (which may well be in that optimum thickness range) it can be pretty handy, especially as it also blocks the wind. Radiant barriers have been tried in sleeping bags a few times in the past: most successful ones I experienced were made by Moonstone Mountaineering back in the early 80's,(my retail days) using a perforated aluminized mylar. they put a 1/2" thick layer of polarguard on the inner side of the mylar, them more polarguard outside of it . It worked pretty well, but experience showed that the aluminized coating was not durable enough - it washed off and wore off - so they dropped the idea. I had a friend who worked at Moonstone, who got me some of the mylar, and I made a bag out of it with just a nylon fabric lining, and slept in it in my typical summer backpacking clothes down to about freezing. Again, my clothes were just about the right thickness to keep the reflective surface at the optimal distance. So it is a useful concept in some very limited circumstances.

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#126120 - 12/30/09 10:14 PM Re: aluminium heat reflection [Re: Paul]
skinewmexico Offline
member

Registered: 09/23/08
Posts: 81
I had a 2# sleeping bag from Herter's in the 70s with some kind of aluminized inner coating, it worked amazingly well.

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#126128 - 12/31/09 01:13 AM Re: aluminium heat reflection [Re: chris angus]
Jim M Online   content
member

Registered: 11/23/03
Posts: 266
Loc: Kitsap Peninsula, WA
I did quit a bit of reading and even read some scientific studies on the subject of vapor barriers. The claim that insensible sweat stops when the temp is right and you are in a vapor barrier does not seem to be true. Also, in actually experience the mylar blankets are flimsy, noisy, and two people who used them in an emergency told me they were not impressed. Perhaps they are worth their weight (2.5 ounces) to carry, but not to be relied on as an emergency shelter and they provide about zero insulation. I liked many of the responses here. Thanks for the topic.
_________________________
Jim M

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#126192 - 01/02/10 12:19 PM Re: aluminium heat reflection [Re: Eugene]
sarbar Offline
member

Registered: 07/15/05
Posts: 1453
Loc: WA
Originally Posted By Eugene
Slightly off topic, but I found a bivy that used to have a reflective coating. It'd be interesting to find out why they got rid of it. I imagine it's because the coating was rubbing off and making shiny sleeping bags.
http://www.titaniumgoat.com/Bivy.html

@Tango
I'll gladly share when my plans firm up more.


It is because the fabric is no longer made. I used the same fabric for our UL FBC Cozies. It works fantastic. I bought up what I could find and when I ran out...yeah, it sucked running out!
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Freezer Bag Cooking, Trail Cooking, Recipes, Gear and Beyond:
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#126193 - 01/02/10 12:24 PM Re: aluminium heat reflection [Re: sarbar]
sarbar Offline
member

Registered: 07/15/05
Posts: 1453
Loc: WA
On mylar....there are fabrics that due use mylar to create a usable fabric. For example is InsulBright, which we use to insulate our FBC Cozies. This fabric is mylar that is then needle punched with poly. So you have a finished fabric that reflects heat but also breathes and is flexible without crinkling. It is also washable.

Does mylar work? Yes and no. You have to use it correctly and plan for condensation. One trick I have used with E-blankets (the cheap ones) is to line my tent floor with one in cold weather, then my sleeping pad goes on top. This barrier stops the cold from coming up. I can sit on the tent floor in bare feet and have no cold. Fantastic for staying warmer out there. The key is I don't sleep directly on it! By having my gear on top, well raised, my evaporation during the night is blown away by breezes coming through the tent and my back is never directly on the mylar.

So don't say no to using it - but do think it out.
_________________________
Freezer Bag Cooking, Trail Cooking, Recipes, Gear and Beyond:
www.trailcooking.com

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#126194 - 01/02/10 12:43 PM Re: aluminium heat reflection [Re: chris angus]
DJ2 Offline
member

Registered: 01/06/02
Posts: 1347
Loc: Seattle, WA
Stevenson Warmlight used to have a sleeping system made entirely of foil. If I recall correctly it was suspended within the tent and, they claimed, eliminated the need for a sleeping bag.

I think it consisted of multiple layers of foil suspended in a way that kept them separated from each other.

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#126255 - 01/04/10 12:50 PM Re: aluminium heat reflection [Re: DJ2]
chris angus Offline
newbie

Registered: 12/25/09
Posts: 4
Loc: england
Thankyou all for your replies much appreciated.Re Sarbar and your post above thats exactly why i bought the foil blanket to go under my sleeping mat as i hope it will stop the cold coming up and to a much lesser degree reflect any body heat.I got this one here in england and although very light seems very strong.Thanks again to you all i will use this site again for sure.

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#126256 - 01/04/10 01:30 PM Re: aluminium heat reflection [Re: chris angus]
Eugene Offline
member

Registered: 12/26/09
Posts: 60
Loc: San Diego, CA
Cold doesn't "come up". Heat is what moves, not cold.
_________________________
www.eugeneleafty.com

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#126259 - 01/04/10 02:42 PM Re: aluminium heat reflection [Re: chris angus]
oldranger Offline
member

Registered: 02/23/07
Posts: 1735
Loc: California (southern)
I just dug a curiosity out of my gear closet - a blue foam pad with aluminized mylar (or something very similar) attached to one side. It was left to by a visiting Japanese colleague. Does anyone have experience with something like this? I think I will take it out next week and give it a try.

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