Insulating with Air?

I heard today that a tiny air space an 8th of an inch thick between two large sheets of drywall is actually a MUCH better thermal insulator than an air space 3 inches thick.

Why is this so???

Is there any research on the *optimal* thickness for this purpose?

 

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Well, first of all, air is a very poor conductor of heat. Therefore, it has the potential to be a great heat insulator. The problem with a space of free air is that if there is room for the air to circulate, it will do so: On the warm side, the air will rise, and on the cool side, it will sink. This circulating air will transport heat energy across the space.

If the air space is quite thin, like 1/8 inch, the friction against the surfaces will keep the air from circulating. So, there is an optimal air-gap, which would be something like 1/4", somewhat depending on the surface properties of the sides of the space.

Actually, most insulating materials are really ways of keeping a lot of air, without allowing it to circulate.

As an interesting side-note, water is also a poor heat conductor, so if you can keep it from circulating, it is a pretty good insulator. This is the reason a wet-suit can keep you warm.

Hans

 

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Ever hear of Aerogel?

Aerogel is a manufactured material with the lowest known density of any solid. [1] It is derived from a gel in which the liquid component of the gel has been replaced with a gas. The result is an extremely low-density solid with several remarkable properties, most notably its effectiveness as a thermal insulator and its extremely low density. It is nicknamed frozen smoke,[2] solid smoke or blue smoke due to its translucent nature and the way light scatters in the material; however, it feels like expanded polystyrene (styrofoam) to the touch.

Aerogel was first created by Samuel Stephens Kistler in 1931, as a result of a bet with Charles Learned over who could replace the liquid inside of a jam jar with gas without causing shrinkage.

Its the stuff at the bottom of the brick holding it up.

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http://en.wikipedia.org/wiki/Aerogel

 

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Excellent...thanks!

Any idea what the optimal space is...between drywall facing exterior walls?

And why not just use many sheets of plastic (vapour barrier) instead of fiberglass?

 

If only it were cheap!

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You're welcome!

No, I have no idea, but I would guess at around 2cm.

Well, the problem is exactly the vapour barrier problem. A sheet of plastic is air-tight, but not entirely. There will be some change of the air inside, and if air comes from the hot side and gets cooled off, there will be condensation.

Therefore, the ideal system has a vapour barrier as close to the warm side as possible, and an air-permeable insulation layer that is vented to the cold side. This will keep the insulation dry.

Hans