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liv4huntin
2004-12-07, 23:55
Hello, new to site and looking for info. Has anyone tried to use a aluminum reflector similar to window heat shield or RV window shield or Aluminum insulation for a sleeping pad? I have read that some folks in cold weather are using these reflectors along with pad for snow camping and bivies. Any thoughts or comments. Thanks Liv

Lanthar
2004-12-08, 01:50
The reflective nature of the pad won't do anything to decrease your heat loss to the ground (I don't particularly want to get into heat transfer physics right now, just trust me). However, they are light weight, inexpensive, insulating pads that will work decently well. But they'll be no more effective than a decent closed cell foam pad.


Hello, new to site and looking for info. Has anyone tried to use a aluminum reflector similar to window heat shield or RV window shield or Aluminum insulation for a sleeping pad? I have read that some folks in cold weather are using these reflectors along with pad for snow camping and bivies. Any thoughts or comments. Thanks Liv

parkender
2004-12-08, 07:20
Hi

This subject has been given heavy duty thought in the following links

http://hikinghq.net/hammock/hammock2.html#Tip%204

http://www.hennessyhammock.com/reflector.htm

and also in the Keeping Warm and Dry section of Hammock Camping below although depending whether you are hammock or ground camper will decide which option to go for. I myself have a Hennessy Hammock (newly aquired) and am in the process of experimenting with various reflectors and pads in my back garden before I venture out properly in Spring (I'm in the UK). So far I've managed to sleep extremely well with no mat/reflector in the hammock and also with just a closed cell foam camping mat - but the temperatures have only gotten down to 3-4 degrees C. I'm waiting for some really cold weather before trying my (homemade) reflector sandwiched between bubble wrap to see how it performs. I'll let you know how I get on!

peter_pan
2004-12-08, 07:55
Reflector pads in hammocks don't cut it below 55-60F. You will need more for an early Spring start as a hammocking NOBO.

Lanthar
2004-12-08, 12:46
Unfortunately, most people don't understand that there needs to be more than simply air space for radiant cooling / heating to happen. There also has to be a significant temperature difference between the two surfaces that are seperated.

As soon as you're wearing clothes, and / or wrapped in a sleeping bag, and / or in your hammock (or in your tent), the surfaces that "count" for radiant heat loss no longer have a significant temperature difference.

Want proof? next time you're sleeping in the cold reach your hand out and touch the OUTSIDE surface of your sleeping bag... what temperature is it? Unless it's in the 70+ deg F range, you're not getting appreciable radiant heat loss.

Formally, radiant heat loss depends on the difference of the FOURTH powers of the absolute temperature in Kelvin (32F=273K).

So, if you stand naked in your tent when it is 20 deg out side, you will have a radiant heat loss factor of 304K(98F)^4 - 266K(20F)^4 = 3.5 billion (of course you have to convert that so units...) between your skin and the ten walls. If you put on a single layer of t-shirt thickness, it will have a temperature of roughly 60F or so (that why you'll still be really cold, you're losing heat to it through conduction, and its losing heat through convection, but there may be some radiant still...), but the radiant factor will have dropped to 288K(60F)^4 - 266K(20F)^4 = 1.8 billion. Now let's put on a layer of fleece, the external surface temperature of the fleece is likely 30-35F (that's why snow won't melt of the outside of fleece if it's cold out, you have to brush it off). Now the radiant factor will drop to 272K(30F)^4 - 266K(20F)^4 = 0.46 billion. Now let's wrap you in a sleeping bag and pad, now the external surface temp MIGHT be all of 22F... 267K(22F)^4 - 266K(20F)^4 = 0.075 billion... 3.5B vs 0.075B (... you don't have appreciable radiant heat loss when you're in a sleeping bag and have ANYTHING beneath you - ie, even the fabric material as the suface temp will be 22F or less do to convective heat transfer)

and BTW... less than an inch of "dead air space" from a foil bubble pad isn't enough either because you get a LOT of convective and conductive heat transfer that heats up the air in the bubbles, then they stay warm when it's that little air... (the same idea in high loft sleeping bags... except air bubbles can't compress)

EDIT - Morale of the story is "A little knowledge is a dangerous thing."

SGT Rock
2004-12-08, 14:52
Great posts. The whole concept of radiant heat loss is overblown, otherwise we would have all traded in our sleeping bags for those emergency blanket sacks a long time ago.

woodrat
2004-12-16, 17:50
i recently aquired a emergeny bivy bag , hope to test it this winter will let you know results, woodrat

Lanthar
2004-12-17, 23:09
going to use it in a hammock? or on the ground? with or without a supplemental pad?

woodrat
2004-12-19, 22:28
hopefully all of the above, I want to make a couple of my own, so I bought this one to test out, see what I like and do not like about it. any input from others on this subject greatly appreceated.

Lanthar
2004-12-19, 23:12
woodrat, I have a couple of suggestions for your tests... I'm going to assume you are using a sleeping bag... use the one you have, but also test a homemade one made out of simply a couple of sheets of the thinnest painter's drop cloth plastic you can get... I believe you'll find that the main benefit of the emergency bivy is due to it being vapor & wind impentrable... the mylar may have a slight advantage, not due to the reflectivity but due to the slightly more rigid nature of the material...


hopefully all of the above, I want to make a couple of my own, so I bought this one to test out, see what I like and do not like about it. any input from others on this subject greatly appreceated.

woodrat
2004-12-20, 23:08
Thanks Lanthar, the emerg. bivy bag I bought is A16 from campmoor, pretty nice, heavy duty, has a fleece(sorta) linning. we will see if its as tuff as they say.! I plan to try it alone, then with a fleece sleeping bag inside, etc. And yes I have about 15 different sleeping bags, trying to weed some out.! Like to get down,(pardon pun), to about 10. I never thought I would say this, but I have too much gear.!!

Lanthar
2004-12-21, 12:35
oh, so you don't have just the mylar one? nice...

Iceman
2004-12-24, 12:04
Been snow camping for a few years, here is what I have learned, take two cheapo Walmart 1/2 inch blue foam pads per sleeper on ice/snow. Ten bucks, and you will be all warm and fuzzy. Or one foam pad and one thermarest. If the thermarest holds pressure, you will be a bit warmer, than the two blue pads. And, if it blows, you still have the single blue pad, not as nice, but liveable. Two is the way to go. Dont scrimp on the pad weight of two, you will be happy you brought both. Kevin

woodrat
2004-12-25, 02:05
heres something I use for winter camping. I use out dated forest service fire shelter as my campfire reflector, open and rollout, stand it behind fire, support it with 2 long stakes driven in ground, anchor ends with 2 short stakes or 2 metal tent stakes. you will not believe how good this works.!! best part is you can often get outdated ones for free.!!!

Locutus
2005-01-12, 23:50
Early last spring I was trying out a tarp (I had previously only used double wall tents) and got a tad cold in my sleeping bag. So I slipped my mylar space bag over my sleeping bag and that did the trick. I warmed up alright, but eventually it became rather clammy inside the sleeping bag due to the fact that the space bag doesn't breathe. I wonder how a space bag would work INSIDE a sleeping bag as a vapor barrier (and to reflect heat)? There has been a lot of discussion recently about the benefits of vapor barriers as part of a cold weather (winter) sleep system. Incidentally, reflectorized bubble wrap works great as a pot cozy. You can buy custom pot cozies made from this material at Antigravity Gear (http://www.antigravitygear.com/) , or buy a bulk roll of it at Home Depot for about $25.00.

Lanthar
2005-01-13, 01:31
I can buy 2ft width of that bubble wrap for $1.5 per linear foot off the roll... bought some to make a 3-cup ziploc pot cozy, probably won't ever use as much as I bought.

The mylar would work great as a vapor barrier, poor for reflecting heat. The physics just don't work for it adding anything due to "reflective radiant heating" in that scenario. Reflective surfaces work best (aka make the most difference) if you have no other significant insulation source. If you have other insulation sources reflective material are at best a micro-marginal benefit. Most of the benefit you'll see is due to the material's wind-impermiability and vapor barrier.

but, it would make a cheap and effective VB

SGT Rock
2005-01-13, 07:40
I am not as impressed with the bubble wrap version of a pot cozy because of de-lamination I have seen from constant use. Tinman said he had something new to stop this.

Sgathak
2005-01-13, 08:21
Im of the general opinion that a space blankets only serious value is as a wind/waterproof first layer in the construction of a survival shelter.

However, I used to work security on a particular property that sat next to a fairly open, hilly field. I got a few breaks during the shift, that would lump together so I got about an hour of "free time" and would use that time to do 1 of 2 things. Sleep, or play with backpacking gear.

I was given a nice Russian Poncho/Shelter to test and write a review for. Since it could be used as a bivy sack, I decided to kill 2 birds with 1 stone. I took my nap in the bivy sack. There was no insulation, and it was a pretty cold/windy night, but I stayed shockingly warm... except for my butt. My butt froze.

The next night, I tested it out again (this time it was drizzly) and stayed both warm and dry. To keep my butt from becoming permafrosted to terrafirma I used a reflective car window visor. Worked better than I would have thought.

I overslept ;)







(dont worry... I set the alarm on my watch)

Lanthar
2005-01-13, 14:55
I am not as impressed with the bubble wrap version of a pot cozy because of de-lamination I have seen from constant use. Tinman said he had something new to stop this.

hmm.. I wonder if he might be layering an extra layer of tape on it...

blackdog
2005-01-13, 17:04
I used a windshield shade for cooking a couple of meals (lunches) during the summer.

http://solarcooking.org/windshield-cooker.htm

Although the reflective surface of the windshield shade doesn't cut it as extra warmth in cold weather, it worked for cooking food in the sun. The bucket or box that is suggested in the instructions can successfully be replaced by an opened backpack or a rolled foam pad.

I've talked about this before, but some itches don't go away although scratched. Pop-can-burner-mania is another of those itches, I guess.