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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Where I work we have a vacuum, which means there is no air. But we need insulation to separate areas of different temperatures
In a normal situation it prevents two areas of different temperatures (thermal insulation) from mixing and becoming the same.
If you want the hot air outside and the cold air inside. If you had no physical insulation, the air would mix and you would end up with the same temperature air inside your house as outside.
Another thing is insulator does not mean no conduction, it just means it’s poor at doing so. If you leave a blanket in the sun, it will eventually become warm or hot and then stay warm after you bring it in.
Finally there are more properties than just insulation for why a material is chosen. If you have an outside wall. A void with air and then an inside wall, yes the air in the void will be insulation to an extent. But if you have a draft, then a blanket is much better than letting air flow freely between the walls.
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