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 expands and contracts with temperature. This makes it less dense when warmer and vice versa. Hot air rises. I’m sure you have heard of that. This creates a convection current. If we trap air and limit its movement, then air will only transfer heat by conduction and some radiation(everything will radiate heat).
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