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TrailScouter 
Group: Members
Posts: 17
Joined: Nov. 2012
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Posted on: Feb. 10 2013, 12:54 pm |
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In order to better insulate your sleeping system during the subfreezing winter camping nights I know that you should use 2 pads under your sleeping bag. I have always used a closed cell foam pad underneath my primary pad for greater protection.
I've read on the forum that some people feel that it is better to put the closed cell pad over top of their primary pad, but I don't understand the logic in doing that. Your primary pad, say an Exped 9 or NeoAir XTherm, is what is supposed to trap the warm air from your body immediately underneath you, while the closed cell pad is intended to prevent the loss of that same heat to the cold ground below. If you place the closed cell pad overtop of your primary pad I don't see how you'll really receive the benefits of the warm trapped air in the primary pad below.
Tell me what you think and why one way is warmer than the other. Thanks.
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| Post Number: 2
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rayestrella
Group: Members
Posts: 6419
Joined: Nov. 2004
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Posted on: Feb. 10 2013, 2:34 pm |
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Its not a case of what we think, but what is true. Go read about R-Values.
But first you need to realize that the pads you mention are all different.
An Exped Downmat 9 has an r-value of 8, the highest retail backpacking pad going. The down fills the entire air space of the pad slowing cold transfer and increasing resistance. There is no reason to put anything on top of or on the bottom of it really.
A pad like the IAC is air with just a half-inch of insulation bonded to the top of it. For this you would put the closed cell foam pad on top giving the most insulation against your body and making a thicker area with higher resistance.
With a self-inflator like a prolite there is less reason top or bottom, but top will provide a little more resistance because of the holes drilled in the foam.
The XTherm has no true insulation as we are used to thinking of it. Instead it has a bunch of honeycombed layers to create dead-air space and block cold transfer. Plus it has reflective material that returns the users heat. They say their pads have an r-value equivalent, as they won't test out the same way as traditional insulations. With them you want the pad on bottom to benefit from the reflective attributes.
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I measure happiness with an altimeter
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| Post Number: 3
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treelinebackpacker
Group: Members
Posts: 430
Joined: Aug. 2011
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Posted on: Feb. 10 2013, 3:24 pm |
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The idea isn't really that air mattresses will "trap" warm air. In fact, the air inside will generally be cold and circulate beneath you. Your body doesn't produce enough heat to keep that pocket warm. It cools faster than you warm it. This is why air mattresses have insulation in the first place. It's to prevent this circulating air from contacting your body. The insulation is usually something similar to the synthetic insulation that you see in sleeping pads. It's fibers slow down air movement and trap some heat in little pockets that the insulation produces. This slows air movement, thus slowing the loss of heat. Heat wants to diffuse from an area of high concentration, to an area of low. Insulation works to slow this down.
Foam will actually trap and retain some heat in tiny air pockets within the material. This is why people like it against their body. Imagine a foam cup. They generally hold heat very well. You can have scalding water inside, and not be burned outside. an inch of this goes a long way.
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| Post Number: 4
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johnq62
Group: Members
Posts: 379
Joined: May 2009
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Posted on: Feb. 10 2013, 3:35 pm |
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I use a Exped 9 year around, during the summer I really never "feel" more warmth compared to a non inso pad
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| Post Number: 5
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no_granola
minor deity
Group: Members
Posts: 12659
Joined: Dec. 2004
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Posted on: Feb. 10 2013, 4:46 pm |
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In winter, the closed cell foam IS my primary pad. I put a prolite on the bottom to give myself more padding.
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The difference between people who think for themselves and those that follow the herd is that thinking people aren't afraid of reality.
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| Post Number: 6
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vinovampire
Winter is Coming
Group: Members
Posts: 645
Joined: Dec. 2007
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Posted on: Feb. 10 2013, 5:36 pm |
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Last night, I used a 3/4 length Therm-a-Rest RidgeRest (R=2.8) on top of a Therm-a-Rest NeoAir All-Season (R=4.9). My GF used a thick, older Therm-a-Res inflatable pad (R-value unknown) with a full-lenth Zrest (R=2.6) on top. We slept on snow in a single-wall tent in temps somewhere between 0 and -5 degree F. We both felt warm and toasty all night.
My impression is that it doesn't really matter which pad is on the top/bottom, unless you're concerned about punctures. In that case, you have to ask yourself whether you're at a greater risk from sharp objects above or below.
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| Post Number: 7
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toesnorth
Group: Members
Posts: 2520
Joined: Jan. 2007
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Posted on: Feb. 10 2013, 8:20 pm |
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Just got back from a semi-monthly trip and had temps from highs of mid-20's to lows of around 5 to 10.
Exped downmat 9 with repair kit, no spare pads.
Well, we sledded the dog along and he has a z-lite.
If my pad failed beyond anything the repair kit could handle I'd steal my partner's exped. He'd handle it better than the dog.
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"Failure is never as frightening as regret."
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| Post Number: 8
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GottaGamble
Group: Members
Posts: 1321
Joined: Sep. 2009
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Posted on: Feb. 12 2013, 1:45 pm |
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2 or 3 weeks ago, I was testing my quilt out for the night..15 degrees. Notice my air pad on the snow and foam pad,3/4 length, on top of it. It worked, I was fine all night.
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www.mybackpacking.blog.com
"A government big enough to give you everything
you want is strong enough to take everything you have."
Gerald Ford
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