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 good insulator because of how few particles exist, which means it’s less likely for them to bounce and pass on heat, whereas a solid is all joined together, so if one end heats up, it moves through the metal easily.
But air is also fluid, which means it’s constantly moving around, meaning it will pass on the heat or take it away frequently.
If you have trapped air in between two solids, you have a very good insulator.
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