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
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
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.
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).
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.)
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
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
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.
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.
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