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  1. #21
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    Quote Originally Posted by Knotty View Post
    As mentioned by some, dead air is what insulates. Down works by creating many tiny pockets of air that minimize convection. Ziplock bags won't work, other than the benefit of being a vapor barrier. Even air mattresses used in cold weather need to have something inside of them, like the Exped DownMat, otherwise the air convects and provides very little insulation.
    my recent experience(post 13 above) suggest that ziplocks filled with only air does add more insulateing value then a vapor barrier alone.the two bags that went flat would have still served as vapor barriers yet i definatly felt a chill there.the areas of the two full ones i stayed warm.same bags, more air.
    i am not saying air is as good as other insulation.but i wonder how big the differance really is.
    diyin to hang

  2. #22
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    Did a little research trying to find the difference in R-value between an air space and an insulated air space. The paragraph below sums it pretty well.

    The air space in our house varies, but in generally measures about 2″ deep offering a paltry R-value of about .80. In contrast, if this same 2″ cavity was filled with fibreglass insulation, this R-value could be increased substantially to about 8.0.

    Other sites suggested that an air cavity o 1-4" had a value of R-1 (not far off from the .8 above)

    So yes, the ziplock bags do add some insulation value, just not very much.

    Sometimes experimenting is half the fun.
    Knotty
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  3. #23
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    knotty thank you for you participation .i value your input very much on any subject that may come up here.i have been looking around the enet and have not come across any consistant values.from r.4 per inch in the article you state up to r6 per inch.th most common i found is r1 per inch. i also found that article you quoted from.seems to be a homeowners opinion. in it (comments section)someone else states r5.6 per inch for dead air space.
    http://www.oldstonehouse.ca/day-to-day/dead-air-space/

    most places agree there is no dead air space. if there is differing temp on either side there will be a heating to cooling current inside the space.makes sense to me.something like this.


    so now my questions are
    if the space was really tall woud that process take longer,or will the action speed up in proportion?(i do not know if this relates,but it poped into my head)seems if it takes longer the rvalue is differant for differant height air spaces?
    if you roll that picture so the heat is on top(me lying on an air mattress) how does that affect the action?the heat is allready on top so it seems the same heating to cooling current would not happen.or it would be much slower.
    so if you turned the model cold side up(air overquilt) it seems like it would really loose heat fast.as all the heat would rise up to the cool side and be cooled, to quickly fall to the hot side....
    if i filled a 2.5 gallon bag with air,put a few down feathers in it and pressed it against the window could i see these currents at work?

    here is another link of a guy who tested a bunch of insulations.this test really gives my air for insulation quest a black eye,but it is interesting.
    http://www.cockeyed.com/science/insu...sulation07.php
    diyin to hang

  4. #24
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    Now there's a guy having fun with science, or at least pseudo-science.

    I was surprised that the goose down results weren't as good as expected but on page 5 of the testing he says the feathers got wet and "The wet feathers were not as effective, which allowed more ice to melt, wetting still more feathers. The problem was snowballing, although that is a poor metaphor for this situation."

    Have fun with your own experiments.
    Knotty
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