Insulation: Air vs. fibreglass, styrofoam, etc.

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Why particularly do you suspect the people you are indicting (without evidence)? Please defend your thesis with actual data.
HB
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Vacuum is best, with two reflective sides. I never figured out argon a heavy gas. I think air with humidity is worse than dry air. Syrofoam is a little bit worse than some other foams. I could never figure that out. Fiberglass tends to be a little worse than cellulose because cellulose stops air flow better. I also think extra thin fiberglass is better. Corning used to make very fine, no itch. Insulating the roof will shorten the life of shingles, they get hotter. Maybe if every building had reflective or plants, the world would cool down.
Maybe someday I'll install reflective sheeting on the house like I did on garage. First I need to cut openings in the wooden sofet where they installed perforated aluminum over the wood. Well they did drill a couple holes in the wood, here and there. Bought the house like that.
Greg
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Neither fiberglass nor Styrofoam are "solid". They are basically air with a tiny bit of structure to keep that air from moving (much)...
Even if your attic were hermetically sealed, the air in it would be moving all over the place (though too slowly to notice).
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Exactly. And they rely on the fact that stationary air is in fact a poor conductor of heat.

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wrote:

Another way to explain it is that there are two variables that control how effective trapped air can be as an insulator. One is preventing mixing and convection -- movement of the air, for practical purposes. Therefore, small pockets are more efficient than big ones. The other is the relative conductivity and relative volume of the entrapping medium: Plastics usually are better than glass, which is better than metal, etc.
So fine, closed-cell foam is an extremely efficient insulator. Fiberglass batts are relatively less so, but still are quite good because a dense network of it is very good at preventing internal movement. Nanogel, which is a type of aerogel, is one of the best that use air as the insulating medium. (Most other aerogels have another gas in the pores.)

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On Fri, 29 Jul 2011 12:39:46 -0400, Ed Huntress wrote:

I contend that as a practical matter, "small pockets are more efficient than big ones" does not remain true as cell size shrinks to zero. Instead (for any given medium and filler gas) efficiency improves as size decreases to some point, after which efficiency gets worse, due to increased importance of heat conduction relative to convection as size decreases. With an ideal medium, the ratio need not change, because ideally the ratio of gas volume to medium volume can remain constant as cell size shrinks and as constant strength (or, at least, constant cross section of medium) is maintained. But as a practical matter, after cell wall thickness reaches some minimal amount, it cannot shrink further as cell size decreases.
[snip re aerogels & nanogel]
Makers of "cenospheres" are quite proud of their products -- see eg <http://www.isbu-info.org/all_about_ceramic_insulation.htm and <http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address 5x89276>
--
jiw

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wrote ...

Sure. But the R value of polyurethane foam, for example, increases as the pore size diminishes to the practical minimum you can obtain and still have continuous foam.
But that practical limit diminishes further with aerogels, including nanogel, because the thickness of the entraining walls can be vanishingly small. And then you get even better R values.

<http://www.democraticunderground.com/discuss/duboard.php?az=view_all&address 5x89276>
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And that is the reason that polyurethane foam is a good insulator. Not the size of the bubbles.
Dan
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wrote:

It's both. After three years or so, much of the HCFC in polyurethane foam diffuses out of the foam and is replaced by air. Typical board-type polyurethane insulating foam loses a couple of points of R-value in the process, from, say, R-9/inch to R-7/inch. Obviously, the speed with which this happens depends on the thickness of the foam, its closed-cell integrity, etc. But those are typical values.
But R-7 is still very high, and it's the result of the material at that point, and its structure.
--
Ed Huntress



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