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.
Well, they actually do use air as insulation for windows.
The thing is, there are better gases than air, (78% of air is nitrogen), but they use mostly argon as the insulator on windows because argon is much denser than nitrogen which is in the air.
Additionally, argon actually blocks UV rays as well as noise. Argon was discovered by Sir William Ramsey in 1894.
Note: Krypton is even better than Argon in all of the properties I have mentioned, it is more expensive and not as readily available as Argon though.
My brother-in-law did not insulate his roof because “air is the best insulator”.
Now, when he heats his house, the hot air rises, and exits his house through the roof.
You need to keep the air where it is, that’s wat insulation does.
Very good question.
Air is actually used as insulator in many applications.
Antenas one such example (search for microstrip and stripline).
Air is not so good at stopping conductive solid or liquid objects from touching a live wire, however. Thus, electric wires are in insulator sheaths.
Air is a great insulator, but only if it’s sitting still. Moving air takes heat with it, so it’s sort of a crappy insulator. Think about how nice a cool breeze feels on a hot day. That’s moving air taking the heat away from you. Still air holds a little bit of heat, so it works pretty well. Think of that same hot day, but without the breeze. Insulation, like fiberglass or cellulose, mostly just holds air in place so it can insulate.
Now we could seal the walls up so air couldn’t move, but that would be pretty expensive, and would cause other issues, so it’s better to just use insulation.
Solid insulators can hold stuff together. Fluid, like air, can’t. Likewise, a vacuum can’t either.
Also, the characteristics of air can slightly change based on environmental factors, which can impact how good of an insulator is.
Edit: Lol! I totally thought this was about electrical insulation!! Leaving this here since every silly is a valuable silly.
Air isn’t really that great. The highest end home insulation you can get are vacuum insulated panels which is where they put a low density foam inside of a bag and suck out all of the air. It’s many times better than standard insulation, but it’s obvious Achilles heal is nails.
Because air is only a good insulator in a lab or in theoretical physics. In the real world, it’s a terrible insulator.
Air is a good insulator, but because it’s fluid it can form convection currents which are good at moving heat. What the insulator does is to try to immobilize the air as much as possible to prevent the formation of these currents.
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