This has bothered me ever since I first heard the phrase as a kid.
If air is a good insulator, why do we fill things with insulating material? (Ex: walls with fiberglass, coats with cotton)
I realize these things are very porous, so hold a lot of air. But by them being used at all, must mean air isn’t that great on its own.
Is it just a matter of air is only “good” and other stuff is just even better? Or is it just considered good by being a bad conductor?
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Air is a great insulator, but only if it’s sitting still. Moving air takes heat with it, so it’s sort of a crappy insulator. Think about how nice a cool breeze feels on a hot day. That’s moving air taking the heat away from you. Still air holds a little bit of heat, so it works pretty well. Think of that same hot day, but without the breeze. Insulation, like fiberglass or cellulose, mostly just holds air in place so it can insulate.
Now we could seal the walls up so air couldn’t move, but that would be pretty expensive, and would cause other issues, so it’s better to just use insulation.
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