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  1. #1

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    Air mattress in sub-freezing temperature

    There has been some threads about air mattresses talked here, but not really systematic review about how they cope with sub-freezing temperature. I have now tested two air mattresses in sub-freezing temperatures and with bad experience.

    In both cases the problem seems to be air circulation. Part of the mattress is always in area where it will get exposed to freezing cold air, that area will freeze, after that air moves and my back gets chilly, I myself do not move at all. Chilly is never so cold that it would freeze me, but after few hours of constant regular chills in my back every 5-10 min it gets Me eventually. In my last experiment I did get warm in a minute after I deflated the air mattress and slept warm the rest of the night (had also UQ).

    Is there difference in mattress fill? Should the mattress be left half empty to make air circulation harder?

    As You can guess my theory is that in tent use temperature difference is so small that thermal pump effect does not happen.

    Please keep this thread a sub-freezing temperature only. The colder the better!

    First example -8 F:
    GEAR: Thermarest Trailpro Large (open cell foam filling with web like cut holes to make mattress lighter)+ Hennessy winter double system (2 x pads and two undercovers) + synthetic winter sleeping bag under me + 3-season down bag over me + over cover.
    RESULT:
    Back chills but feet and upper side very warm.

    Second example 19 F:
    GEAR: Exped synmat 9 Deluxe pump, Warbonnet winter Black mamba TQ, Warbonnet winter Yeti UQ.
    RESULT:
    Back chills but feet an upper side very warm, after 2 hours instant warmness after deflating mattress practically empty while laying on top of it.

    In my opinion open cell foam mattress without those cuttings is too heavy.

    MY NEXT MOVE?:
    Should I get Exped DOWNMAT 9 deluxe pump or settle with closed cell foam pad? (I think in winter time some kind of pad is always needed for emergency and cabin use. Exped would mean smaller back size and better sleep in cabin but more money spent)
    Last edited by voivalin; 12-08-2010 at 23:40.

  2. #2
    Senior Member
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    I would have just used the winter yeti without the pad. I've been into the low 20F range with a 3 season JRB, which has half the loft of the yeti.

    For the subzero temps I would have tried the winter yeti plus the mylar liner plus some extra clothing and a winter TQ.

    There is a paradoxical effect with too many layers - I used to bundle up like crazy because I am always a cold sleeper. I now sleep with either a mid weight or heavy weight base layer and a fleece 'clava or hat I can pull over my ears, and appropriately rated quilts. Your body has to provide all the heat. If all the body's energy are trapped in multiple layers of clothing, or on top of a heavy mat or pad, it's not getting to the down and the underquilt isn't doing anything.

    A synmat 9 has an R rating of 4.9 - the downmat 9 has an R rating of 8. So I suspect the downmat would be a better choice for winter temps. An alternative would be adding a CCF pad to the synmat - R values are cumulative for pads, and a 3/4 inch thick CCF would add about 3 to the 4.9 of the synmat.

  3. #3

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    My final goal is to build a simple as possible hammock system that keeps me relatively warm at temperatures -15 F. And alive at -40 F.

    That is why I used air mattress + Winter Yeti at 20 F even when Yeti alone is rated to 0 F. And I think Your idea that UQ was useless in my second example is correct. Very good and obvious idea - but I did not figure it out myself.

    Better R rating of the DownMat does not solve the problem with circulating air IMHO. But maybe down compared to SynMat filling is better in circulation prevention also. It would cost me 204 € to test that.

    One more route to go would be full length UQ either alone or suspended loosely under Yeti (...and closed cell pad for rescue and cabin use).

    At this moment I think I probably go CCF-pad route and think full length UQ later...

  4. #4
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    a full length winter incubator with 900 fill + overfill has got to keep you pretty warm...

    you can always try to suppliment your yeti with insultex (discussed at length at hammockforums.net)

  5. #5
    MAD777's Avatar
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    Even as a former ground dweller, I found that air mattresses had their limits as far as insulation goes. And, they are relatively heavy. Trust me though, I was using them in any temperature, just for the comfort. As the conditions got colder, I would add CCF pads for the warmth needed.

    In a hammock scenario, I just don't think air mattresses are good, on many levels.
    1. They don't insulate well.
    2. You don't need the padding for comfort
    3. They are narrow and narrow pads of any type are challenging in a hammock
    4. They are heavy, more than many under quilts
    5. And you have to blow them up

    Shall I tell my ground dwelling friends to start watching ebay for a gently used air mattress?

  6. #6

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    No ebay

    Shall I tell my ground dwelling friends to start watching ebay for a gently used air mattress?
    No eBay for My mattresses (I have two of them). They are very cosy when used in tent. My tent has never been so warm and dry before I used two of those monsters during our last trip. They covered whole tent floor and as I said cosy, warm and no condensation - our body heat kept even outer tent almost dry. Two people and 25-30 F temperature during night.

    It has been bit of a bummer that they do not work that well in hammock.

    Pumping those up makes You feel warm before going sleeping bag, no need for warm up walking. I think that kind upper body work-out is actually much better than even running to keep the warm up and blood circulating after days hike.
    Last edited by voivalin; 12-09-2010 at 07:34.

  7. #7
    Senior Member Just Jeff's Avatar
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    I've used the Downmat 7 comfortably at a windy 20 and just started a little chill at 14, but it would have kept me alive and still sleeping there. I wouldn't say airmats are a bad idea for hammocks at all...some people prefer them, like slowhike.

    Air circulation is part of the issue, and I think a higher R-value would help an airmat stay warmer in a hammock. Technically, I think it's radiation that causes an airmat to lose so much heat in winter, but it's enabled by the convection inside the pad as you described. Add to that the convection on the underside that experience in hammocks and we need more insulation at a given temp...but that applies just the same to underquilts.
    “Republics are created by the virtue, public spirit, and intelligence of the citizens. They fall when the wise are banished from the public councils because they dare to be honest, and the profligate are rewarded because they flatter the people, in order to betray them.” ~Judge Joseph Story

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  8. #8
    slowhike's Avatar
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    I use the Exped DAM 7 regularly, even in my bedroom. I've used it along w/ a full length UQ (JRB Rocky Mt No Sniveler) down to about 10°f, & could have been comfortable at lower temps. How low? Don't know w/o trying it.
    But Personally, I like the comfort of a DAM (softly inflated) in the hammock, as well as the idea of having that extra cushion in the unlikely event that I would need to sleep on the ground.

    A couple of the regular trade offs I clearly see are...
    Having to inflate/deflate
    A little dampness on my back because it's non-breathable, but synthetic clothing makes that a temporary issue.

    I think fully enclosing the DAM in a full length UQ goes a long way in taking you to lower temps, & the Down insulation is obviously rated for colder temps.
    I've found that system to be very versatile by (like you mentioned) loosening the UQ, or removing it if need be.

    Adding the ccf pad to the system would defiantly be my choice considering the temps you mentioned.
    don`t leave the CREATOR out of the creation!

  9. #9
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    Downmat 9

    I also have a Downmat 9 that I've used in my JRB Bridge down to 6 degrees F in reasonable comfort. I inflated it fairly hard, and it's intriguing that deflating it might not affect the warmth that much. I find that deflating it slightly also helps the mat to wrap around me a bit for warmth (my pad is 25" wide).

    I plan on trying a NeoAir with a thin foam mat as an alternative to the Downmat.

    I agree completely on having a subzero forum for northern dwellers - please keep it up.

    Doug

  10. #10
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    Both the UQ and the air pad are providing insulation by trapping the warm air that your body has heated.

    I think that the air in a pad can circulate a little bit so the whole air pad is trying to equalize so that the air temp cloest to you is basically the same as the air temp on outside edge.

    I think the air in an UQ is more fixed and therefore there will be more of a temperature gradient across the UQ which means the temp of the UQ closest to you is warmer than the temp of the UQ at the outside edge.

    So I think an UQ is always a better insulator in a hammock if it has enough loft compared to the outside ambient temps. But if your UQ alone is not enough than adding the air pad helps more than it hurts.

    I think your experience also highlights that fact that sleeping on snow requires a whole lot less insulation than sleeping in the air. Your pad set-up that works well on snow in a tent doesn't fair well in a hammock, even with an UQ.

    ONe nice thing about winter hammocking with pads is if I am too cold I can go to ground and add the UQ to my top side insulation and rely on the pads and the snow to be adequate under me. Or build a fire...

    Anyway...

    My first suggestion would be to use supplement the air pad with a CCF pad with an egg crate design like the TR Z-rest or the GG Nightlight. The CCF pad goes on top.

    I have found the CCF pad on top of the air pad to feel warmer than the air pad on top of the CCF pad.

    My second suggestion is to add a windshield to the UQ. I have one of JRB's old weathershields that have a "breathable" strip of material along its length.

    Of course, you should have a closed tarp arrangement that minimizes heat loss due to the wind [convection]. But even with that, I find a wind shield mounted at the UQ to be effective. Some people have experienced condensation but I haven't. I do leave a loose fit / small gap between the wind shield and the UQ. I am not trying to trap heat as much as I am trying to keep the wind from infiltrating the UQ.
    Love my JRB BMB

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