wrote in message
...
On Jul 28, 11:49 pm, Larry Fishel wrote:
On Jul 27, 10:20 am, "Existential Angst" wrote:

It would seem that if air itself was so good, solid insulation wouldn't
be
so high a priority

Neither fiberglass nor Styrofoam are "solid". They are basically air
with a tiny bit of structure to keep that air from moving (much)...

Exactly. And they rely on the fact that stationary air is in fact a
poor conductor of heat.

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.)


Even if your attic were hermetically sealed, the air in it would be
moving all over the place (though too slowly to notice).