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  1. #51
    Senior Member greggg3's Avatar
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    PE sheeting - this is basically visqueen were talking about right? its essentially incompressible. And while it was what I used for years for a ground sheet (as recommended by colin fletcher) until I switched to tyvek, it did essentially nothing as far as insulation - its only 5 mils thick ( I think I used 6 mil, but whatever). I still think there is something going on regarding units or something because I find it hard to believe 4 sheets of visqueen = 3/4" foam pad (of course I've been wrong before, just saying)

  2. #52

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    Quote Originally Posted by greggg3 View Post
    PE sheeting - this is basically visqueen were talking about right? its essentially incompressible. And while it was what I used for years for a ground sheet (as recommended by colin fletcher) until I switched to tyvek, it did essentially nothing as far as insulation - its only 5 mils thick ( I think I used 6 mil, but whatever). I still think there is something going on regarding units or something because I find it hard to believe 4 sheets of visqueen = 3/4" foam pad (of course I've been wrong before, just saying)
    We're talking PE foam, not sheeting/visqueen.

    So you have 4 deferentially cut foam layers plus small air gaps between each layer. The air gaps is where most of the insulation value comes from.

    My problem with IX, is that everything has to be just perfect to maintain the gaps and a snug fit (UQ) to realize the insulating potential of this system. I believe many people do not get it perfect (myself included) and that is why such a wide low temperature range is reported.

  3. #53
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    Quote Originally Posted by greggg3 View Post
    I guess it just doesn't sound right to me - I don't know about IX but I am very familiar with sleeping on PE sheeting. I'm almost certain that I'd be warmer on a 3/4" foam pad than I would on 4 sheets of 5 mil PE sheeting. Based on the R values however that were quoted, it says that 4 sheets of PE would have an R of 3 while a 3/4" thick z rest pad only has 2.2 Doesn't this seem wrong to you all?
    well, remember, the R-value for both those products were almost certainly produced by different companies under different testing conditions, so the likelihood of their R-values being thusly comparable is slim. Also, from my understanding, even if they were, you can't exactly add R-values together like that anyway because boundary conditions between materials also affect R-value.

    it's a very complex exact science, and I think us backpackers try to make it more simplistic than it is, to the detriment of it being truly beneficial for us. it may be good for rough guesses, but I would not trust any of our calculations without field testing.

    so in the end, your hunch is probably way more on the true side for all the in-exactness of what we try and do with poor standards in testing, etc.

  4. #54
    MacEntyre's Avatar
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    Quote Originally Posted by gmcttr View Post
    The air gaps is where most of the insulation value comes from.
    The 'air gap' that people refer to when constructing IX UQs is the tiny spacing (~1/16") that we like to maintain between layers in order to insure that there is no compression of the PE foam. Those air gaps are not there to insulate; they help optimize the insulation value of the PE foam itself.

    Quote Originally Posted by gmcttr View Post
    My problem with IX, is that everything has to be just perfect to maintain the gaps and a snug fit (UQ) to realize the insulating potential of this system. I believe many people do not get it perfect (myself included) and that is why such a wide low temperature range is reported.
    IX is reasonably forgiving unless you operate at the edge of the envelope. IX by itself is not a good choice for freezing conditions, so of course, folks will have trouble as they approach that limit.

    A well constructed, differential cut IX UQ with good pattern shaping, many darts and adjustable channels, will go a long way to helping you find comfort below 40*F.

    - MacEntyre
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  5. #55
    New Member Yetee's Avatar
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    Quote Originally Posted by greggg3 View Post
    PE sheeting - this is basically visqueen were talking about right? its essentially incompressible. And while it was what I used for years for a ground sheet (as recommended by colin fletcher) until I switched to tyvek, it did essentially nothing as far as insulation - its only 5 mils thick ( I think I used 6 mil, but whatever). I still think there is something going on regarding units or something because I find it hard to believe 4 sheets of visqueen = 3/4" foam pad (of course I've been wrong before, just saying)
    The R value for IX that I came up with was calculated from the CLO value of 2.0 that the manufacture advertises. The R value of 2 layers of PE sheeting came from greenhouse studies and is based on the assumption there is an air gap between the two pieces (this is how cheep greenhouses are done, much like double pane windows but much cheaper). If you laid two pieces of 5 mil PE sheeting down and laid on top of it you would not have any where near an R value of 1.5 that was stated. Also something I forgot to mention in the other thread was PE sheeting has diminishing returns, so 4 layers would not necessarily get you an R value of 3

  6. #56
    MacEntyre's Avatar
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    Insultex has been tested as house wrap, and given an R value of 2.8.

    When I bought a roll of 1/32" PE Foam, it came with a data sheet that had an R value of 3.




    P.S. ...sure is confusing having all this discussion of PE sheeting mixed in with discussion of PE foam.
    "We must, indeed, all hang together or, most assuredly, we shall all hang separately." - Ben Franklin
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  7. #57
    New Member Yetee's Avatar
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    Quote Originally Posted by MacEntyre View Post
    Insultex has been tested as house wrap, and given an R value of 2.8.

    When I bought a roll of 1/32" PE Foam, it came with a data sheet that had an R value of 3.




    P.S. ...sure is confusing having all this discussion of PE sheeting mixed in with discussion of PE foam.
    I agree, I didn't mean to be the cause for confusion, but since my thread got dragged into this I thought I would try and clear it up with where I got the values from. I wonder why the insultex web site lists a different value. unless I am calculating wrong, (2.0 Clo * .155 rsi/Clo)/(0.1761101838 rsi/rValue) = 1.76 rValue. I suppose they could just be trying to be on the cautious side with the 2.0 Clo, or just different methods of testing the different products, I would be currious if the IX house wrap is made differently than IX used for clothing and quilts.

  8. #58
    Senior Member DemostiX's Avatar
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    Quote Originally Posted by MacEntyre View Post
    A well constructed, differential cut IX UQ with good pattern shaping, many darts and adjustable channels, will go a long way to helping you find comfort below 40*F.

    - MacEntyre
    I take it you mean by that ".....helping you find comfort at temperatures as low as 40*F and maybe lower," not that Insultex performance shines below 40*F.

    I suspect lots of expectations of performance of some of these thin insulators is the experience of magic and faith remembered and witnessed from childhood with metalized "space blankets."

  9. #59
    MacEntyre's Avatar
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    Quote Originally Posted by Yetee View Post
    ...I would be currious if the IX house wrap is made differently than IX used for clothing and quilts.
    It's the same stuff.

    Quote Originally Posted by DemostiX View Post
    I take it you mean by that ".....helping you find comfort at temperatures as low as 40*F and maybe lower," not that Insultex performance shines below 40*F.
    You are correct!
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  10. #60

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    Quote Originally Posted by MacEntyre View Post
    Insultex has been tested as house wrap, and given an R value of 2.8.

    When I bought a roll of 1/32" PE Foam, it came with a data sheet that had an R value of 3...
    I understand and believe that IX can work well for quilts.

    What I don't understand is an R value of 2.8-3 when you consider that 5/8" of Dow Styrofoam also has an R value of 3.

    From my experience with both materials, I am very confident that the styrofoam has a much higher ability to slow heat transfer.

    The testing methods and parameters must be completely different and therefore void my understanding of R values as it would pertain to IX.

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