Oct 21, 2011 at 1:36 am #1280915
I’ll try to explain myself. I’m getting older and a simple CCF just doesn’t do the trick anymore. So I bought, a few years ago, a BMW TorsoLite and use this ON TOP of a Therm-a-Rest Z-Rest (the old blue/black one). Seemed logical to do it this way because the TorsoLite provides the necessary comfort and the Z-Rest protects it from being punctured. But……
According to the recent SOTM report about Lightweight Inflatable Sleeping Mats, both Will and Roger seem to do it the other way: they put the airmat of choice on the ground and then use a thin CCF as overlay on top.
I have no doubt the CCF will boost the thermal insulation of the airmat (more so if this is just a plain air core inflatable with no insulation at all) but why would the position make any difference? I understand that, theoretically, the R-values are accumulative and, if that would be true, position should be irrelevant. Am I wrong? My gut feeling says I am wrong indeed, but I don’t understand why.Oct 21, 2011 at 6:58 am #1793359
but, the ccf will trap warm air better, w/ the inflatable the air is going to cool through the night
I've read a dozen or so "experiments" folks have conducted and they all concluded ccf on top for warmth, I cam to the same conclusion
obviously a ccf pad on the bottom provides protection for the inflatable, but at the cost of some warmth- if you need both- make a "sandwich" a light 1/8" pad on the bottom, inflatable, suitable r value pad on top :)Oct 21, 2011 at 7:04 am #1793360
CCF on top insulates you from the cool air in the pad. Underneath, you're against the cool air in the pad, which is cool due to exposure around the edges. And I am an engineer, but not a good one, and I really never paid much attention to that thermodynamic thing. Not once I graduated anyway.Oct 21, 2011 at 7:45 am #1793377
@retiredjerryLocale: Oregon and Washington
I think Joe has it
Air pad is exposed to cold air around the edges. Air currents inside the air pad move the cold to the middle under your body.
If the air pad had insulation in it, then this would reduce the air currents inside the pad, so maybe it would make less or no difference.Oct 21, 2011 at 8:41 am #1793405
@bestbuilderLocale: Pacific Northwest
Henk, the BMW TorsoLite in a self inflatable pad- it has foam inside, so it is a good insulator.
You can use it either way without a noticeable temperature difference. There is minimal air movement in that pad. The issue comes up with a true inflatable pad (which the BMW isn't) because of air movement and convection/radiation heat loss.
When you body tells you its time to move to a thicker pad these issues will then come into play. That would be a good time to review the report form Roger and Will very closely.
In my own experience I find the having the CCF on top is warmer for me.
I'm not and certified engineer, just a certified gear tester geek.Oct 21, 2011 at 9:50 am #1793426
@halfturboLocale: Northernish California
This is from the Therm-A-Rest FAQs (emphasis added).
"For the ultimate, ultralight solution to cold weather sleeping, travel with a small ProLite, ProLite Plus, or NeoAir mattress (depending on temperatures), coupled with a full-length RidgeRest® mattress as a bottom layer. In addition to the essential comfort you need in the hips and torso that this top layer provides, you also get the ultra-efficient boost of warmth from closed cell foam, along with the protection you need for open bivies on bare ground or on ledges."
RickOct 21, 2011 at 9:51 am #1793428
@hhopeLocale: East Bay
I've been wondering about this question too, but in regards to open cell pad like prolite.
Glad to see others are wondering too. Since air movement isn't as much a question, having the closed cell pad on the bottom struck me as having advantages, with a gossamer gear type 1/8 pad, it's also nice because that pad material isn't very slippery on silnylon floors.
But I was wondering about the real physics of it, I know there's an actual answer scientifically. What strikes me is that the cold source is primarily the negative radiator of the ground, and that's what you are insulating against. So with open cell air pad, it seems like it would be better to have the closed cell under it, to slow the cold air entering into the open cell air pad, which then acts as loft does, holding in your body's heat. Blocking your body's heat from that layer doesn't seem intuitively sensible for closed cell/down, loft type air pads. The sides don't seem to matter that much in this scenario.
But it's just speculation, I like having the closed cell to protect the air mattress and stop the sliding, but I have been curious about how the R values and the cold from the ground and the heat from your body really work together in a scientific sense. Too bad I don't have a lab, a walk in freezer, a thermal dummy, and measuring devices.Oct 21, 2011 at 10:03 am #1793431
@dwambaughLocale: Pacific Northwest
I wouldn't worry about it too much unless the conditions are extremely cold. I too would prefer to save the Torsolite from punctures. If you wake up some night and find your bottom cold, it would be a great time to experiment — shuffle the deck and see what happens!Oct 21, 2011 at 12:28 pm #1793484
@tbeasleyLocale: Pigeon House Mt from the Castle
I too have been thinking about which side is it best to place a CCF mat on my NeoAir.
On a recent snowshoeing trip in the Australian Alps, I took my NeoAir regular and a ¾ length 7 mm thick 72 gram closed cell mat, my sleep system was WM Flash Jacket and Pants, WM Summerlite Sleeping bag and a PBL 180 quilt. I did not have thermometer with me but on the first night we camped between Australia’s two highest mountains it was cold enough for my Coleman Extreme stove on a full canister of Coleman Max fuel to struggled to work, I estimate it was around -15C or less, I used the CCF on top and I was cosy warm.
TonyOct 21, 2011 at 1:22 pm #1793509
@rcaffinLocale: Wollemi & Kosciusko NPs, Europe
I tend to agree with Joe. I am not sure it makes a huge amount of difference though.
CheersOct 22, 2011 at 2:24 am #1793675
I don’t have much time now — I’ll be away for the weekend and only connected to see whether there were any answers. Well — I’m impressed. Didn’t think this thread would get much response. Only demonstrates I’m not the only one who’s “worrying” about the position of both mats.
I should have been a bit more explicit about my reasoning behind putting up this question and would like to do this now but, because of lack of time, I’ll just give a few hints (I’ll come back after the weekend). Tad wrote: >When you body tells you it’s time to move to a thicker pad……< Well, that time has come already. Due to the fact that my Z-Rest is old (likely) and the TorsoLite too thin (maybe), they don’t give me enough padding, so I wake up several times at night because of sore hips and shoulders (I’m a side-sleeper). At 5:00 or 6:00 I don’t know how to position myself so I have to get up; even though that ain’t too bad because it makes me being earlier on the trail again :), I really would prefer to sleep all night like I do at home.
The easiest solution would be buying several mats (one for each occasion), but I don’t like to fill my gear closet with a huge amount of items: As a minimalist I prefer to have as little as possible and make my gear work for me. I could buy a DAM for winter (sleeping in the snow), but I know I won’t need that much thermal insulation the rest of the year. So…… I’m about to buy a full length, plain air core mat to give me the comfort I need (as I’m getting older, it won’t get any better) and boost the insulation with a CCF (or even two, like Mike suggests — making a sandwich).
Before deciding on anything, I’d like to know IF the position of the mats matters and if so, WHY? I mean a solid, well reasoned “scientific” answer (if there is any). As I said before, my gut feeling is that it does make a difference (and I would think a bit more than just a little); Joe’s explanation is only one of the reasons that occurred to me. Beginning of this week I opened a “conversation” about this in another forum here in Spain where I exposed my vision about this “dilemma” and I would have liked to translate my reasoning here and now but…… lack of time makes me having to postpone this until after the weekend. If anyone speaks Spanish and has A LOT of time (I copied and pasted the conversation into Word-format and resulted to be 26 pages long — yes, 26), this is the link:
Please, help me out before I make the wrong decision. Many thanks in advance.
Edit to explain: TFD = The Flying Dutchman = El Holandés Errante (in Spanish) for anyone who would like to open the other thread — I repeat, this is VERY long (you're being warned, don't shoot me).Oct 22, 2011 at 8:33 am #1793720
Convection/conduction/radiation. I vaguely remember those concepts. For some reason, however, I do have vivid memories of 25 cent Lone Star and tequila shots at Coldwater Country. Ahhhh, college.
Skip to the recommendations – Exped Synmat 7 UL. And a 1/4" CCF pad from Gossamer Gear.Nov 11, 2011 at 9:41 am #1800782
@owareLocale: Steptoe Butte
If you take a doublewide but thin ccf pad, you can fold it in half and sandwich the inflatable in the middle.
Help keep the inflatable from stick/rock/cactus spine punctures, AND your body away from the air currents and subsequent cooling by convection inside the inflatable.Nov 11, 2011 at 10:56 am #1800807
@servingkoLocale: Intermountain West
I have been using a syn ul7 with a Gossamer Gear 1/4" pad under or on top. I didn't really notice a great deal of difference in warmth. I much preferred it on the bottom since it greatly reduced sliding around and as a side benefit it should offer puncture protection.
As a side note, it isn't as warm as my Kookabay DAM, nor is it as comfortable, but it has certainly earned a spot in my gear closet.Nov 11, 2011 at 11:19 am #1800818
With a ccf pad on top, I think the air inside the airpad says pretty cool. So there won't be a lot of covection along the sides of the airmat.
If you put the ccf pad on the bottom, the air in the airpad will be warmed by your body and there will be significant convection along the sides(and exposed top portions) of the airmat.
So I would expect the warmer option to be a ccf on top.
The thicker the airpad, the more pronounced this effect should be.
Think of it this way: If your airmat was 5 ft thick, its pretty intuitive that a ccf on the bottom of it won't keep you warm. A ccf on top of a 5 ft thick mat would keep you warm.Nov 11, 2011 at 11:36 am #1800822
I suppose you talk about the Exped Syn Mat UL7; indeed there shouldn’t be much difference having the CCF on top of below IF you’re using an airmat WITH some kind of filling, because the filling should stop (or at least reduce) the convective heat loss. Whether this filling is down or synthetic is irrelevant — well, in reality it isn’t because down would be better but…. that’s not the point I’m making. I’d like to know whether it could be important when using a full length, plain air core mat (without fillings).
Copy/paste from my second post on this matter: >”So…… I’m about to buy a full length, plain air core mat to give me the comfort I need (as I’m getting older, it won’t get any better) and boost the insulation with a CCF (or even two, like Mike suggests — making a sandwich).”<
Under normal circumstances (3 season-use) I’d definitely put the CCF below to offer puncture protection (as you say). My quest is really about what to do in winter (on snow) when my mayor concern becomes the thermal insulation and, at the same time, I’m not that worried about punctures.
Thanks for your suggestion. It’s more or less the same as what Mike came up with in the first answer on my initial question (sandwich the inflatable between 2 layers of CCF pads — the top one with a sufficient, appropriate R-value). To be honest…. as I haven’t received any *scientific* answer on my question about what will be better in terms of thermal insulation, the *sandwich* idea is what I’m pondering right now.
Since nobody came up with a clear answer, I suppose I’ll be wrong in assuming there should be a difference in between having the CCF on top or below. Having said so…… I understand that, theoretically, the R-values are accumulative but I can’t believe that, having the inflatable on top, with my body tossing und turning all night and therefore stirring up the air inside the inflatable, that this won’t have any influence on the relative warmth the inflatable could/should provide to my body (in reality, since the air inside the airmat will be colder, it will be robbing heat from my body -all night-). On the other hand, if I put the CCF on top, I do believe (maybe/possibly I’m wrong) that, no matter how much I move during the night, there won’t be any convective heat loss BECAUSE this CCF consists of thousands of tiny little bubbles that are not connected with each other. Furthermore, once I can heat up the upper part of the CCF (spending a lot of energy, precious calories, in doing so) it will stay warm at the moment each and every bubble has reached its thermal equilibrium in relation to the bubble *next door* (at least that’s what I think).
Once again, I really think that this subject is of importance (at least to some degree) because IF position matters, one could get away with a thinner (lighter) mat if same would be positioned right. And this would make it possible to REDUCE our overall pack weight.Nov 11, 2011 at 11:45 am #1800828
@woodenwizardLocale: Greater Mt Tabor
aint science- but air pads can feel cold to the touch. CCF on top don't feel cold.
sorry for the short post :)Nov 11, 2011 at 11:55 am #1800835
>” So I would expect the warmer option to be a CCF on top.“<
You’re my man!!! At least somebody who seems to think like I do (and so is Mike, and Joe, and Jerry, and…….); if we could only find somebody who could explain this scientifically.
Sorry I couldn’t include this in my previous post; I was writing same whilst you posted yours.
>“….. air pads can feel cold to the touch. CCF on top don't feel cold…..”>
You are right, for sure, and don’t feel sorry about your post being short. Each and every input is appreciated.Nov 11, 2011 at 12:07 pm #1800837
@Henk My description was intended to be a lay engineering description if not purely scientific. I try to keep away from talking about temperature gradients in normal conversation any more. I could try to but not sure I still have it in me. I am a recovered engineer.Nov 11, 2011 at 1:21 pm #1800858
I can understand one wouldn’t want to go too deep into some aspects when in *normal* conversations. Don’t worry, I’m not gonna make you…. (I can’t anyhow, but I wouldn’t, even if I could).
I have now *formally* decided I’m going to buy a no-fill airmat with 2 *thin* CCF (⅛ & ¼) to do several experiments this coming winter; i.e. ⅛ or ¼ or both underneath, ⅛ or ¼ or both on top, ¼ underneath and ⅛ on top and/or, last but not least, ⅛ underneath and ¼ on top. My personal *feeling* is that “both on top” will be the best (in that is provides better thermal insulation) and “⅛ underneath and ¼ on top”, a close second. I'm convinced that "both underneath" will be the worst of all options. (Edit to add: Sorry, only one ⅛ underneath will obviously be even worse.)
I anyone wants to chime in and give a thorough scientific explanation, it might save me buying either the ⅛ or the ¼ CCF, because…… once the main question has been resolved, I’ll still be stuck with the question of how thick the CCF will have to be to guarantee appropriate (not too much, not too little) thermal insulation. (Edit to add: I wouldn't mind it being too much, but then I'm carrying unnecessary weight and that's exactly what I'm trying to avoid.) My *intuition* says neither of the two will be enough; I'll probably have to buy thicker ones :(Nov 11, 2011 at 1:34 pm #1800864
Sounds like fun Henk. Most here are well outside the normal realm and your experiment plan proves it for you as well. Those trained as engineers think they can predict the behavior of physical systems without experiments based on modeling. Engineers are sometimes wrong. I will be interested to hear your results.Nov 11, 2011 at 6:55 pm #1800941
Dave- that's a good idea on one large pad folded over- like it :)
MikeNov 11, 2011 at 7:53 pm #1800951
I've followed this topic through several threads over two years or so. I'm leaving myself vulnerable here but: I've always thought that ground convection was by far the greatest factor in heat loss for pads. My experience certainly points to this. So: put the ccf pad under the airmat. Inhibit the ground convection. I own a synmat 7 ul; perhaps the loss of heat from the sides is greater than I picture because of the thickness of the mat. But come on: without a ccf pad the whole of the mat is resting on the cold cold ground.
Go easy on me if I'm simply not grasping basic principles here; although I do read and understand Brian Greene (Platonist)and other science writers; but I certainly don't have the math. (And there's nothing wrong with being a Platonist.)Nov 11, 2011 at 7:57 pm #1800953
It sounds like the insulative value should be the same for airmat on top of CCF and airmat underneath CCF once the mats have been warmed by your body heat. I wonder, however, if putting the CCF, which has relatively little mass to warm up, on top gets you to the perception of warmth faster than putting the airmat on top, which has a greater mass to warm.
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