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  1. #1
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    Determining insulation thinkness

    I was on http://www.owfinc.com and found this formula for calculating temperature rating:
    http://www.owfinc.com/Fabrics/insulation%20ETR.htm

    How does this apply to hammocks? Hammocks get colder than tents right? Should I add 20 degrees or so? I don't want to sleep in less than 32 deg. F.

    Two layers of .8 Primaloft would give me an Effective temperature rating of 36 deg F. Is that 36 degrees for real when it comes to hammocks?

    ETR = 100 - (40x1.6 thickness)

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    IMHO hammocking temp rating are the same as tenters. The difference comes into play on bottom insulation and convection heat loss. If you take away the cooling from the wind underneath, just treat the bottom insulation the same as the top. Where thickness is concerned.

    In terms of convection, a large tarp, site selection, a ccp at colder temps, and hammock sock/travel pod will work to defeat the convection. With a 32 degree rating underneath, this would only come into play on windy cold nights or nights below the rating. Throw in a ccp and you will be good to go.
    Is that too much to ask? Girls with frikkin' lasers on their heads?
    The hanger formly known as "hammock engineer".

  3. #3
    Senior Member blackbishop351's Avatar
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    I also wouldn't pick Primaloft for use other than in clothing, but that's just me.
    "Physics is the only true science. All else is stamp collecting." - J. J. Thompson

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    Senior Member hangnout's Avatar
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    I also wouldn't pick Primaloft for use other than in clothing, but that's just me.
    Why not? My bag uses primaloft and works well.

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    Senior Member blackbishop351's Avatar
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    Quote Originally Posted by HANGnOUT View Post
    Why not? My bag uses primaloft and works well.
    My Marmot bag uses Primaloft too - but the insulation structure inside is WAY too difficult for me to try and reproduce in a quilt. I'd like to give you some specific examples, but unfortunately none are coming to mind right now. After having read some articles and comments though, it appears that Primaloft is intended for use in thin layers and does not work as well as Polarguard or Climashield in sheets. The end result is more weight for comparable insulation value, when you're using a simplistic construction method. That's obviously just paraphrasing though, and I could very well be mistaken. Look around for yourself. I do know that both KAQ and Ray Jardine use and swear by Polarguard.
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  6. #6
    Senior Member Just Jeff's Avatar
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    As I understand it, PL is a looser sheet so it drapes better for clothing but isn't as durable when compressed/uncompressed like quilts and bags are. When used for a quilt, it needs quilting loops closer together than PG.

    I made two insulated hammocks (that haven't gotten much use) and two kids quilts (that have a fair amount of use) from PrimaLoft...it seems to work fine to me. (Down is a much better choice for the hammocks than any sheet insulation, though.) Haven't used Polarguard on anything so I can't really compare.
    “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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    Senior Member Frolicking Dino's Avatar
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    I made a permaloft quilt a while back - still have it and it is OK, but not good weight to warmth ratio. I did it because many years ago my dear departed MIL told me the male dino was allergic to down. It turns out he isn't so my next quilt will be down.

  8. #8
    As far as I know, the loft requirements for hammockers as opposed to ground dwellers is the same, except that it has to cover your bottom as well.

    I think that the Beyond Backpacking formula is incorrect. This formula rates only 2 inches of loft to 20 degrees:
    100 - (40x2)=20
    However, the temperature ratings chart seen in Hungry Howie's down quilt guide, Mark Verber's sleep system page, and the specs for Speer Peapods all suggest that 2.5 is a more acceptable amount of loft for a 20 degree bag.

    If you don't expect to go below 32 degrees Fahrenheit, then 2 inches of loft would be about the norm, according to the sources I linked to above. However, everyone sleeps differently, and while this is a good guideline, in the end you may need more or less loft depending on how warm or cold you sleep.

  9. #9
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    Quote Originally Posted by tamboo View Post
    As far as I know, the loft requirements for hammockers as opposed to ground dwellers is the same, except that it has to cover your bottom as well.

    I think that the Beyond Backpacking formula is incorrect. This formula rates only 2 inches of loft to 20 degrees:
    100 - (40x2)=20
    However, the temperature ratings chart seen in Hungry Howie's down quilt guide, Mark Verber's sleep system page, and the specs for Speer Peapods all suggest that 2.5 is a more acceptable amount of loft for a 20 degree bag.

    If you don't expect to go below 32 degrees Fahrenheit, then 2 inches of loft would be about the norm, according to the sources I linked to above. However, everyone sleeps differently, and while this is a good guideline, in the end you may need more or less loft depending on how warm or cold you sleep.
    Thanks. I was wondering if that formula as off cause I was getting like 4 deg F at 2.4 inches. That just seemed too good to be true.

  10. #10
    Senior Member Frolicking Dino's Avatar
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    The female dino formula:
    Start with the temp at which you can sleep at home without cover while clothed as you will be for sleeping while hiking. For me, this is 63 F
    Subtract the lowest temp that you plan to encounter using the quilt / underquilt (lets say 20 F)
    Divide by 10 and then subtract 1 - this will give you the number of inches of loft needed.
    63 - 20 = 43 / 10 = 4.3 - 1 = 3.3" of loft

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