Improving sleeping mat R value.

Discussion in 'Sleep Mats' started by liamarchie, Nov 19, 2016.

  1. ADz

    ADz Thru Hiker


    I would never use a foil blanket above me. I've used them in past to just possibly insulate mat from cold floor?
  2. Rog Tallbloke

    Rog Tallbloke Thru Hiker

    What we think of as cold, say zero centigrade, is only 37C cooler than our core body temperature. I say only, because in terms of absolute temperature on the Kelvin scale (same as centigrade but starting at -273 or absolute zero) it's a small percentage difference. Radiation is proportional to the fourth root of temperature, according to the Stefan-Boltzmann equation. That means the difference in the amount of energy radiated by a 'cold' zero degree surface (ice) and a 'warm' 30C surface (your skin), isn't actually all that much. This is why fiddling around with foil doesn't do much for you compared to improving the R value of the insulation layer which reduces rates of energy conduction and convection.

    Here endeth the lesson.
    Teepee and ADz like this.
  3. Rog Tallbloke

    Rog Tallbloke Thru Hiker

    That's the point really. It's the foam on the foil blanket which does the insulating, not the reflective surface. The silvering does reflect some energy back, but notalot...
  4. Imperial Dave

    Imperial Dave Trail Blazer

    laminate floor underlay works for me
  5. guaruska

    guaruska Backpacker

    I don't have any suggestions to a solution other than using a ccf under the air mat. Now, I use an exped downmat ul 7. Last week I went wintercamping and temperatures dropped to at least -28C (almost -20F), the coldest night. Although I didn't have problems in my sleeping system, after packing camp I discovered that the snow under the mat had melted a little. This means that my heat moves through the mat and melts the snow, obviously. My thoughts on this is that I'm actually "losing" heat that i'd preferebly use within my system. This melted snow obviously freezes to ice after I get up in the morning and ice has a worse r-value than snow.
    Another issue, that might become disturbing in colder temps, is condensation downwards. Has anyone experienced this and has a solution to this? As stated before: ice has worse r-value than snow. I guess circulation of air underneath would be a solution, wouldn't it? I have home made sub-100 g full length 6 mm ccf that I could modd (even more) to get better circulation and perhaps transport the humid air away from body/ground.
  6. Teepee

    Teepee Thru Hiker

    Snow will conglomerate in the night due to it being compressed by bodyweight and rubbed by the sleep mat, it'll form an icy skin even when it's way below -30c with compression and no heating. Even though, the snow has an icy skin, it's never very thick and will only pass it's heat energy to the underlying snow (if it's deep enough). It's precisely this melting that shows the snow is insulating. Even at the end of winter in places that regularly see -40c and below, it doesn't usually get any colder than -10c inside the snowpack. The amount of icing you are seeing is not dependant upon the ambient air temp. If that snow warms to -7c, it will start melting as it's moved and compressed

    Not once have I woken up without a little bit of ice melted on to the bottom of a sleep mat whilst sleeping on snow, it's quite normal IME.

    Adding an air gap that encourages air movement will reduce the warmth of the mat, as it will introduce convection to rob heat from the underside.

    My Downmat 9 is pretty toasty at -40c on the ground, quite comfy. In the hammock, with unlimited convection underneath, it starts to feel a bit cold at around -15 to -20c.
    guaruska likes this.
  7. guaruska

    guaruska Backpacker

    Good explanation. The icy crust is natural due to pressure then. Still the condensation on tent floor must be from the dew-point laying outside the system (mat included). Is this preferable or is it preferable that dew point is inside sleep system...that is within a thicker mat, for example? Cuz the ice, either from condensation or the crust on the snow is, during the day, gonna acquire the ambient temp, right? While the snow is gonna insulate better, and like u said, stay warmer than ambient temp.
  8. Toot

    Toot Backpacker

    First attempt at replying to a thread on forum pages, so let's see if it works... I'd be interested to hear thoughts on this curved ball in the thread, but don't wish to disrupt the current flow.

    Whilst I recognise Downmats et al as wonderful things, I commonly use a self-inflating mat (Multimat Superlite 25S) - three-quarter length, diamond-cut foam internally with a few breaths needed for full inflation. I wanted a compact mat and felt that a foam core still offers some insulation if I get a puncture. Usual use is on Dartmoor, year-round, in all conditions.

    I'm aware this mat has far from the highest R-value and I don't see how that can be changed, but I have found its insulating effect can be improved significantly by a particular method of use so I sleep warmer and I wonder if that has further application. One of the problems I always found with mats is coming off them and finding myself on cold-sapping ground in the night. Even a mat with the highest R-value doesn't insulate if you're not actually on it! One night I got so frustrated with the wandering Multimat that I put it inside my sleeping bag so I was bound to lie on it - easy enough as it's mummy-shaped and only 25mm thick. This gave a notably warmer sleep, and I wondered why.

    I think it's because body-heat warms the air inside the mat, the sleeping-bag provides a thermal barrier between cold-sapping ground and the warmed mat so the mat tends to stay warm and I'm insulated from the ground by a warm-air foam-filled layer with more insulation beneath that, rather than by a colder-air foam-filled layer due to being in contact with cold ground and which the sleeping bag is squished onto by body-weight when the mat is beneath the bag. I realise the mat-in-the-bag method puts the sleeping-bag in closer contact with cold ground so perhaps it seems a counter-intuitive move, but remember I'm not lying against the bag but on the warmed mat above it...

    Of course a thick mat isn't likely to fit inside a sleeping-bag along with a body - or if it does the bag material may be so stretched that that the down/synthetic filling doesn't loft as much nor work as well, so mat-in-the-bag is not a method suitable for bulky mats. I'm not sure what the thermal-maths would say about this but I have used the method for about two years and results are so pleasing I wont be using a slim mat in the conventional way again. I don't see why this wouldn't work with thin air-only mats or even with a foam roll-mat - foam is warm to sleep directly on.
  9. guaruska

    guaruska Backpacker

    here's some bout reflective insulation: https://en.wikipedia.org/wiki/Radiant_barrier
    So u need air/space behind it for it to be effective, otherwise reflective capabilities equals pretty much zer0...

    Toot: interesting - insulate the insulation. Not practical with a thicker air mat but cutting the foam to sleeping bag shape doesn't seem to cumbersome. Maybe it also helps to avoid the condensation against tent floor, but also risking the condensation to stay within sleeping. Gotta try to find out.
  10. Toot

    Toot Backpacker

    Condensation in a sleeping bag...

    Our body normally produces moisture on our skin even when we're inactive - it's often called "insensible perspiration", which is not the notable sweat of exercise. Mind you, we can also overheat and notably sweat even due to being in a sleeping bag that insulates so well it has us too warm! Guess where the moisture normally produced by our bodies goes when we're in a nice warm sleeping-bag? That's right - into our sleeping bag insulation. Normal bodily moisture and the salts and oils with it are part of the reason we use sleeping bag liners.

    This normal bodily moisture may all evaporate (which is a cooling process), but the colder ambient temperature gets the more likely it is to condense in our insulation. It is to prevent this moisture from getting into sleeping-bag insulation at all, and thus prevent any moisture from condensing and reducing insulation performance and even freezing, that polar explorers use vapour barrier liners. To an extent use of outer bags may also be an acknowledgement that a body normally produces moisture that can have an effect upon insulation and warmth, but is being dealt with in a different way.

    Have a look at PHD's website amongst others for detail about VBL's if you like, and reflect upon how and why they're used. I really don't want to divert the thread focus from R-values and improving mat performance - it is my finding and method of achieving improved mat performance that I wanted to add for consideration here.

    In response to Guaruska, I think the particular advantage of my method doesn't just come from insulating the insulation (that's what putting a rollmat under a Downmat does), but from warming the insulation and then protecting that warmth. Of course, a rollmat could also be placed under the bag in addition to my current method of mat-use and presumably increase advantage further. Without a VBL my feeling is that moisture in a bag is inevitable and thus condensation too in cold conditions - my focus here remains in improving mat performance and how I do so.
    Last edited: Jan 12, 2017
  11. guaruska

    guaruska Backpacker

    There are studies, although very few and without enough info according to themselves, that deal with the perspiration while sleeping in cold temps in sleeping bags. Most of them show that we loose about 0,4-0,5 liters of water - the first night. The second night is where the problems start and that has mostly to do with handling the cold vs. sleeping bag.
    The sweat vapour doesn't condensate in very cold temps, it deposits - that is it goes from gas to solid without going through the liquid state, iow turns to frost, as we all can see on our tent inner walls and on top of sleeping bag. This also happens inside the sleeping bag if dew point is there and not outside. The above mentioned problem of handling is that the studies were made on expeditions that used heaters inside tents, making the frost melt inside sleeping bags, obviously becoming water - having a negative effect on the insulation, losing the loft - to later in the night (when heater's off) turn to ice. Frost has a much better r-value than solid ice, which in turn has already reduced the loft of sleeping bag.
    The trick in question is still on how to avoid the condensation (not deposition) which at least I get under my air mat. Using a vbl doesn't make sense unless strictly using a down sleeping bag, but in my case I use a combo of down inner and synthetic outer. In the cold temps of last week I could feel frost inside my synthetic outer, but had no effect on my temp limit since I had to take off my base layer with -25C. Also I figure that the air mat is waterproof which means the condensated vapour must come from ambient in tent and not from inside my sleeping system.
  12. Toot

    Toot Backpacker

    Out on Dartmoor Friday night to catch the snow. No condensation noted on the sleeping bag with the mat used warmly inside it. Very little condensation at all in the tent actually. Just sayin'...
  13. Chris2901

    Chris2901 Ultralighter

    My wife uses a 3 mm Evazote mat to boost her STS mat.Nice side effect:Slipping on Silnylon floors is history.
  14. Toot

    Toot Backpacker

    I don't boost my mat as such, Chris, other than using it inside my bag rather than outside (as per earlier post). It stays in place that way and it is warmer in use, so I haven't resorted to the double-mat process yet and will avoid it if I can.
  15. Chris2901

    Chris2901 Ultralighter

    Absolutely ok,it was just a simple and cheap solution with very little weight penalty.
  16. Rog Tallbloke

    Rog Tallbloke Thru Hiker

    @Toot
    I think Big Agnes made some sleeping bags with pad sleeves built into them. I don't think the down went all the way underneath though.
  17. paul

    paul Thru Hiker

    I had the exped 3mm evazote double sheet. Was superb until i did my newborn giraffe inpression whilst wearing snow shoes and put some serious holes in it :D

    still have it for projects not thought of yet :)
    Teepee, edh and Chris2901 like this.
  18. Imperial Dave

    Imperial Dave Trail Blazer

    Boosting using this technique does work and there are a variety of ways of doing it according to taste. For example I have used a GG thinlight coupled with a GG torso length Nightlight pad and slept very well in -10C.

    Interestingly the GG website says this in their blurb for the Thinlight....

    "If you own an ultralight backpacking air mattress, then it should be an indispensable part of your kit - an air mattress alone might slip and slide and leave you freezing from convective heat loss. Place a Thinlight foam insulation pad on top of or underneath your air mattress to prevent sliding and provide insulation"
    Chris2901 and Lady Grey like this.
  19. edh

    edh Thru Hiker

    :rolleyes:.....ummm so GG think GG stuff is great.....OK...:D
  20. Imperial Dave

    Imperial Dave Trail Blazer

    Hulloo Eduardo :)
  21. Chiseller

    Chiseller Ultralighter

    What abaht when you lay a frozen sausage on a sheet of tinfoil.... It encourages thawing by I presume radiation? Or is it conduction... But either way it does thaw quicker.. I.. Presuming it's because it's spreading the cold from. The body... Or like them aluminium pan things... Like a griddle pan... That you can get for helping to defrost a chicken or turkey.... Same effect... Mmmmm just confused myself :writing::blackeye:
  22. Chiseller

    Chiseller Ultralighter

    @Ken T. tha wer lukin fo this thread :cigar:
    Ken T. likes this.
  23. Ken T.

    Ken T. Ultralighter

  24. Chiseller

    Chiseller Ultralighter

    I agree.... I only looked at the first link and my noggin froze!
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  25. WilliamC

    WilliamC Thru Hiker

    Should have used a warmer pad for it :p
    Ken T., Teepee, Mole and 2 others like this.

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