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  1. #11
    Senior Member Muskrat's Avatar
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    . . . and knowing is half the battle !

    Thanks for the advice . . . SB goes under, not over.

    Guess Paul might be hearing from me soon.... BBO sounds like it may be in order here.
    “He doesn't know the meaning of the word fear, but then again he doesn't know the meaning of most words”
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  2. #12
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    SB is more of a vapor barrier than anything else. As such, it should be on the "warm side" of the insulation system.

    Personally I think the reflected heat concept doesn't come into play very much with the way we apply them in hammocks. That only works when there is air space before the SB. Like JayS notes, once you make contact it may well conduct more heat away than it reflects.
    Knotty
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  3. #13
    Senior Member OldMan's Avatar
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    Thanks to all for the replies. Clearly the SB goes between me and the UQ, either between hammock layers or atop the UQ.

    What I am using is not the silver, paper thin and very crinkly space blanket, I have what is billed as a survival bivy. It's about 6 by 6 and folded along one dimension and hemmed across the bottom and 2/3 of the way up the long side and then velcro'd the rest of the way up and across the top. The inside of the bivy has a very thin lining and the outside is a muted silver.

    So what I am thinking about now is to either invert the bivy and insert betweem hammock layers, or actually remove the sitching and lay it out with the lined side (what was the inside) up and insert between layers, giving more coverage. Any issue with that?

  4. #14
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    Now I'm confused.

    Here is my understanding

    UQ = air heats up in the loft and it slowly releases it back to you.
    SB = Vapor barrier so that outside humidity does not come back in to you

    So if you place the SB between the hammock and the UQ does it not defeat (at least to an extent) the purpose of the UQ?

  5. #15
    Senior Member JerryW's Avatar
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    Quote Originally Posted by JohnH View Post
    Now I'm confused.

    Here is my understanding

    UQ = air heats up in the loft and it slowly releases it back to you.
    SB = Vapor barrier so that outside humidity does not come back in to you

    So if you place the SB between the hammock and the UQ does it not defeat (at least to an extent) the purpose of the UQ?
    Actually, the vapor barrier needs to be between the person and the insulation. Much more moisture will get into the quilt from you, than from the outside weather.


    Jerry
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  6. #16
    Senior Member Muskrat's Avatar
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    I'm also thinking that the UQ will warm the bottom side of the SB and transfer heat through the SB thereby still warming the hammocker . . . correct?
    “He doesn't know the meaning of the word fear, but then again he doesn't know the meaning of most words”
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  7. #17
    Senior Member canoeski's Avatar
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    Quote Originally Posted by OldMan View Post
    What I am using is not the silver, paper thin and very crinkly space blanket, I have what is billed as a survival bivy. It's about 6 by 6 and folded along one dimension and hemmed across the bottom and 2/3 of the way up the long side and then velcro'd the rest of the way up and across the top. The inside of the bivy has a very thin lining and the outside is a muted silver.

    ?
    I think I know what you have and I would leave it intact for it's intended emergecy purpose, but frankly it's too heavy and overbuilt for this application.

    I have a "Space Blanket" of similar heavy ripstop material (silver on one side, red or green on the other) that I have regularily used as a ground cloth in my recent grounddwelling/tarp life. Also for hypothermic emergencies, emergency shelter and signal device.

    But for this application (and also for a pocket emergency kit) a thin Mylar one is lighter and cheaper.
    Not all who wander are lost.

  8. #18
    Senior Member canoeski's Avatar
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    Quote Originally Posted by JohnH View Post
    Now I'm confused.

    Here is my understanding

    UQ = air heats up in the loft and it slowly releases it back to you.
    SB = Vapor barrier so that outside humidity does not come back in to you

    So if you place the SB between the hammock and the UQ does it not defeat (at least to an extent) the purpose of the UQ?
    A few thermodynamic principles are in order here. (Disclaimer: I am not a thermodynamic engineer, although my father was. But I did sleep in a Holiday Inn Express once )

    First, heat (energy) loss can occur my any combination of : convection, conduction, radiation, or evaporation. Second, heat only flows from warmer to cooler areas (higher energy body gives up heat to cooler surrounding areas.) In other words, cold never infiltrates your body (even if it seems that way sometimes.)

    I've heard it said that down insulation "radiates warmth back to your body".
    Unless down has some sort of infrared reflection properties, I don't see how this can happen, unless you are dead and colder than your surroundings.

    The silver Mylar acts in two ways: relects heat back in the form of infrared radiation (heat energy) and as a vapor barrier to protect the insulation from absorbing moisture and loosing insulation value. Not in the sense of vapor barrier clothing/bag which reduces body moisture output and with it a great deal of energy. These two VB concepts are often confused.

    HTH,
    ~bill
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  9. #19
    mbiraman's Avatar
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    Quote Originally Posted by canoeski View Post
    A few thermodynamic principles are in order here. (Disclaimer: I am not a thermodynamic engineer, although my father was. But I did sleep in a Holiday Inn Express once )

    First, heat (energy) loss can occur my any combination of : convection, conduction, radiation, or evaporation. Second, heat only flows from warmer to cooler areas (higher energy body gives up heat to cooler surrounding areas.) In other words, cold never infiltrates your body (even if it seems that way sometimes.)

    I've heard it said that down insulation "radiates warmth back to your body".
    Unless down has some sort of infrared reflection properties, I don't see how this can happen, unless you are dead and colder than your surroundings.

    The silver Mylar acts in two ways: relects heat back in the form of infrared radiation (heat energy) and as a vapor barrier to protect the insulation from absorbing moisture and loosing insulation value. Not in the sense of vapor barrier clothing/bag which reduces body moisture output and with it a great deal of energy. These two VB concepts are often confused.

    HTH,
    ~bill
    Good explanation, your room at the holiday inn was well worth it.
    Last edited by mbiraman; 12-07-2009 at 17:39.
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  10. #20
    Senior Member JerryW's Avatar
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    Quote Originally Posted by canoeski View Post
    I've heard it said that down insulation "radiates warmth back to your body". Unless down has some sort of infrared reflection properties, I don't see how this can happen, unless you are dead and colder than your surroundings.
    I'm not disputing this, but when you lay in your hammock and that puffy down underquilt starts doin' it's thing, it sure FEELS like it's reflecting your heat. It even feels like it's generating a little extra. What an incredible feeling!




    Jerry
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