Dec 31, 2011 at 1:21 pm #1283558
Just got some of this at Lowe's for $12 and think it would make a great UL sleeping pad. Planned on using it for other purposes for now so before I buy more, any thoughts? Reflects approx 97% of heat back, comes in varying widths for different sizing, and is really light! Seems like it should work great as a stand alone or to supplement/increase R value on a Neoair.Dec 31, 2011 at 1:28 pm #1817987
Radiation accounts for a small amount of the heat released from the body, so getting 97% of that back isn't very significant. The foil version has an R-value of 0. The double bubble version has an R-value of 3, so that might be useful. I could have sworn someone here tried it, and found that it was heavier than an equivalent foam pad. Can you throw a 72×20" piece on a scale?Dec 31, 2011 at 1:53 pm #1817998
I got the 16" width double bubble with foil on both sides to line a huge 150qt cooler but a 16" x 74" chunk rolls to 4.5" diameter and weighs 6.5 oz. I'm 210 and it seems pretty durable too. I also understand that it wouldn't actually generate heat but would diminish heat loss/transfer to the ground if it reflected 97% of my heat back and kept it in my bag. Correct me if I'm wrong. Relatively comfy too for 1/4" thick.Dec 31, 2011 at 2:34 pm #1818007
That weight is nicer than I thought it would be. Thanks for measuring it.
I believe radiant heat loss is something like 3%, so even 97% of that still comes up with less than 3%. It's better than nothing, but it's not a big deal either.
Edit: Okay, it's more than 3%, but insulation is more important.Dec 31, 2011 at 3:30 pm #1818022
So if you threw this under a standard Neoair, it would still keep you warmer and help minimize heat loss, thus making the Neoair feel warmer, correct? Might make a good pot cozy too as long as you didn't let it come in contact with direct heat.Dec 31, 2011 at 3:39 pm #1818025
It has an R-value of 3, so yes, it would make a Neoair warmer. It should have nearly zero effect as a reflective barrier though. That's because one is already built into the Neoair and because the extra fabric layers and air in the Neoair would absorb the radiation before it radiated to the EcoFoil beneath.Dec 31, 2011 at 9:17 pm #1818120
@ckrusorLocale: Northwest US
The fact that Neoair pads are competitive on a warmth per unit weight basis with pads using other kinds of insulation (foam or fiber) demonstrates that radiant barriers can be effective for sleeping pads. But, for your application, I see several things that might be worth considering.
Sleeping pads containing foam, down, or synthetic fiber insulation are good at impeding convective heat loss to the ground because they contain a very large number of very small air spaces. They are good at protecting against conductive transmission of heat because the solid parts of the insulation (the polyester fibers, down plumules, or foam cell walls) create a "tortuous path". If we imagine heat as a packet of energy travelling through the solid material of the pad, it would have to travel hundreds of meters just to make it through a 2" thick down-filled pad because the plumules are long and the contacts between them are few.
Neoair pads and Double Bubble Ecofoil don't have any of those qualities. The air spaces are large and few in number and the solid path across the material is relatively direct. But they have multilayer radiant barrier films (two radiant barrier layers in the Ecofoil and more than two in the Neoair).
Imagine that a square foot of the surface of a sleeping hiker is radiating 64 watts of heat (this is radiation only). If you put something opaque, like carbon paper, very close to the surface of that hiker (but not touching it), then the carbon paper will recieve almost all of that 64 watts of radiant heat, and it will radiate half of that back to the hiker (32 watts), and half away from the hiker, from the other side of the paper. By adding one opaque radiant barrier layer, you have effectively cut radiant heat loss in half (reduced it by 32 watts). If you add another opaque layer (not touching the first), you cut it in half again, but the real reduction this time is not 32 watts. It's 16 watts. A third layer reduces the radiant heat loss by half again, but this time that's only 8 watts. By the time you have six layers, adding another opaque layer cuts the heat loss by less than one watt. This is a general rule, and it remains true for your application despite complications like aluminized surfaces and thermal bridging between layers.
The Ecofoil probably doesn't actually have an R-value of 3 (the R-values of building insulation is usually grossly overstated). But even if it does, it would only achieve that when it is the only radiant barrier layer. Underneath another radiant barrier (like a Neoair), it would be no better than bubble wrap, which has an R-value of about 1.
So, using a radiant insulator over a conductive/convective insulator (like a NeoAir over a foam pad) works great, because each component takes care of the kind of heat transmission that the other component misses. The other way around (a down air mattress over Ecofoil, say) also works great. But using two multilayer radiant barriers together, like a NeoAir over Ecofoil, will not achieve the improvement in warmth that you might expect given their independent R-values.
I think some of this might just be a restatement of the good points that Eugene already made.Dec 31, 2011 at 9:48 pm #1818128
@mikemartinLocale: North Idaho
A while ago, I got all excited about the "brilliant idea" of wrapping a Z-rest pad in a reflective space blanket to create the ultimate warm/light/foolproof (i.e. non-inflatable) Winter pad. I hoped I could boost the R-2.2 Z-rest R-value above R-3.5 for sleeping directly on snow. I thought the egg crate design of the Z-rest would create perfect airspace pockets to allow the reflective barrier to work its magic against radiant heat loss.
Alas, testing with my home-brew thermal conductivity test apparatus revealed that the R-value of the reflective-wrapped Z-rest was identical to that of a Z-rest simply wrapped in some green non-reflective silnylon. In both cases, the wrap improved the R-value (slightly) over that of a naked Z-rest, but there was no apparent benefit to the reflective wrap.
My search for the perfect Winter pad continues…Jan 1, 2012 at 3:59 pm #1818364
Thanks for the explanation. I wasn't doubting Eugene but a more thorough example of what I envisioned helped immensely. Guess I'll save my money and keep on searching! Thanks for everyone's thoughts and help.May 17, 2013 at 7:10 pm #1987193
@highpeaksLocale: Upstate New York
There is nothing wrong with the insulation and it is insulation, reflective. The problem is the application. By the time the radiant heat, which you are generating, escapes the bag it's mostly lost. The pad will with the barrier reflect the heat, but in all directions. This radiant heat, to be important, needs to be reabsorbed back into the bag to you. Very little in this application. Put the material in the bag and you will notice a world of difference.
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