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 in terms of conduction is a good insulator, because in conduction it’s the bumping into of individual atoms that transfers the heat/energy from one area to another.This works to our benefit in terms of like dry suits and double pane windows because the air can be kept still and can only transmit energy through conduction.
However because gases/air can move wholly (wind, currents, etc.) They can trasmit heat through convection as well. By taking energy at the surface and those energized particles just being moved somewhere else. In a house with no other insulation, the heat inside would convect onto the walls, conduct through them, and then convect somewhere else outside. This makes it not cost effective to use air to insulate houses, because you would have to make a essentially a double layer house that is perfectly sealed between the two layers.
In the case of jackets, they wouldn’t be very flexible and comfortable to wear if they were insulated with air, because to be effective it would be like wearing a bunch of balloons.
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