eli5 | Why does Insulation exist if “air is a very good insulator”?

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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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39 Answers

Anonymous 0 Comments

Because air moves around, especially when there’s a temperature difference.

You don’t want air moving around if it’s going to carry away all the heat you are trying to keep insulated.

So Insulation is often just some solid but very porous material that will hold a lot of air in it and keep it from drifting away, but its still utilizing the air to help it insulated things.

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