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  1. #1
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    This could get deep - Does an R-Rated cold weather air mattress need to be inflated to work?

    I live in western PA and have been enjoying the cold weather. It's been GREAT! Snow and temps dropping into the teens. I noticed something and I wanted to throw the question in my title out there. I have been using my WB BBXLC with a 0 degree Wookie along with a 2QZQ UQP. It's a double layer so I slid my Thermarest NeoAir X-Therm Max pad in between the layers. I inflate it to maybe 30% and I am very toasty. I always bring my down UQ and bag in after I get up and go into the house. I leave the hammock and pad outside hanging under the tarp because I plan on doing it again the following day. I noticed the next night when I was setting everything up and climbing in that the Thermarest pad lost most of it's air - either through a slow release or maybe I didn't have the valve tight - regardless, it was pretty much flat but still in place. I once again slept for HOURS in total comfort and temps were in the 16 degree range. So.... once again - Does an R-Rated air mattress for cold weather actually need to be filled with air to do the part of keeping you warm. I understand w/o air, the comfort level may be suffering, but I want to ask about the air vs no air and does it STILL do it's job. Thanks for putting up with my long winded post! Cheers - Happy Healthy New Year

  2. #2
    Senior Member cmoulder's Avatar
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    When you inflate an air mat at ~95°F (temperature of breath) and it cools down to 15°F it will lose a lot of volume. According to that Bernoulli fella. But of course the air cools rather quickly while you're in the process of filling it, so the temperature contrast is not quite as stark as that. And then your own body heat subsequently warms it back up to around 75°F or so. It's complicated.

    BUT, at roughly 30% inflation you're going to have a lot of cold spots where the body compresses it enough to bottom out, so what you have at that point is basically an expensive vapor barrier.

    Did you get any condensation? Were the sleeping bag/quilt, or clothing or hammock moist in the morning? Maybe try just a sheet of Tyvek and see if you get the same result.

    It seems that with a 0deg Wookie and UQP you should be warm even without the Xtherm. Have you tried that also?
    Last edited by cmoulder; 12-28-2020 at 14:19.
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  3. #3
    dakotaross's Avatar
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    Agreed, you’re probably getting benefit from your very expensive vapor barrier. This is not to say that you’re not getting any insulation. Just that the R-rating is measured on a fully inflated mattress on a flat surface. Not sure what that pad has besides reflective heat radiation, but I know it utilizes that and that specific process could even work better if the space between the heat source and reflective layer is reduced. Needs at least a little space to work. But again, I think it’s mostly the “barrier” properties that you’re benefiting from in that mode.


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  4. #4
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    I asked Sea to Summit this question awhile back and their response is below. The bold is mine.

    Sea to Summit has always tested its sleeping mats for R-Value in a laboratory; to date we have worked with the EMPA labs in Switzerland. Complete, production-quality mats are tested under laboratory conditions which include carefully monitored internal air pressure.

    Because this level of testing was not followed by all sleeping pad manufacturers, REI and MEC (the leading retailers in the US and Canada respectively) formed a working group which brought all brands together to agree on a testing standard (under the direction of the ASTM standards organization). That standard will become effective on January 1, 2020. It will allow consumers to compare R-Values across all brands.

    The tested R-Value of an air mat does decrease as the internal pressure decreases (The Ultralight was tested at a pressure equivalent to 0.7psi which resulted in the quoted R-Value of 3.3).

    However, it is important to know that even with the coming ASTM R-Value standard, the test is a static test. A sleeper moving around on a sleeping pad pushes air around inside the air-filled chambers, and this may result in warmth dissipating from the pad. The Air-Sprung Cell design is far less susceptible to this than many other designs.

    In a hammock two additional factors have to be taken into consideration:

    - the pad may well become ‘kinked’ in places due to the curved surface of the hammock, leading to potential loss of warmth
    (again, the Air Sprung Cell design is less susceptible to this) unless it is restrained in some way
    - the pad may simply slide out from underneath the sleeper

    I trust the above is helpful; please let me know if I can provide additional details (including how R-Values are tested).

  5. #5
    Senior Member BillyBob58's Avatar
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    In my limited testing, I noticed some definite warming with my Neoair All Season with no inflation. As some have said, some of that might have just been the VB effect, as well maybe as some radiant block. But, as you can see from Mando's post, you should expect to lose significant insulation. I can never remember his user name, but there is a fellow here that has done some great testing using an REI bridge hammock and an X-therm, and been toasty at about 11 below zero F. But he has used this pad with less than full inflation, and noticed it was considerably less warm, and not warm enough for temps well above 0F. So, I suspect that with no inflation, you will lose a lot, but not all, insulation. Keep in mind that VB effect alone could account for over 20 degrees worth of protection, good to maybe 50F, plus possibly some radiant block adding a bit more, theoretically at least. Also, you wold still benefit from significant wind block, even with no inflation. So, IMO, better than nothing, but probably never enough except for warmer temps. But as you add enough inflation for even 1/4" to 1/2" loft, things will start warming up noticeably. I'm guessing. Then it will be VB + RB + wind block + X loft.

    EDIT: But here is an idea: you have all of that great cold weather available to you, unlike poor disadvantaged folks like me, so put it to the test for the rest of us! Start with no inflation, then add a bit to see what it takes. Or go backwards: test the X-therm for us full inflation, then slowly let some air out and see what happens.
    Last edited by BillyBob58; 12-28-2020 at 10:04.

  6. #6
    Senior Member
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    Without any air, your pad is essentially a space blanket. Good vapor barrier, no real insulation.

    Also, never use and R rated pad. If kids are around, use the G rated pad. If you have real privacy, get out the X rated pad and have fun!

  7. #7
    OlTrailDog's Avatar
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    It doesn't need to be inflated if you lay it on top of a bed.

  8. #8
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    Hey.... Thanks for the input - Truth is, I was VERY comfortable without it - With it WITH some inflation AND With it W/O Air! I brought this up because on the 2nd or third night sleeping out I noticed that it had lost most of its air and I was too lazy to pull it out and fill it - I even have a battery powered air pump! Regardless - I CAN say that this Hammock camping has bit me and bit me hard. I have people telling me I'm crazy and what.... did the wife kick you out of bed! I TRULY enjoy it. Happy Healthy New Year Everyone

  9. #9
    Senior Member
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    Quote Originally Posted by rickyracer View Post
    Hey.... Thanks for the input - Truth is, I was VERY comfortable without it - With it WITH some inflation AND With it W/O Air! I brought this up because on the 2nd or third night sleeping out I noticed that it had lost most of its air and I was too lazy to pull it out and fill it - I even have a battery powered air pump! Regardless - I CAN say that this Hammock camping has bit me and bit me hard. I have people telling me I'm crazy and what.... did the wife kick you out of bed! I TRULY enjoy it. Happy Healthy New Year Everyone
    It did the same to me...after a week or two of sleeping in the backyard, my husband finally helped me hang my hammock in the bedroom to get me back in the house. Now I’m trying to convert him!

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