Why Are There No Perfect Electrical Insulators?

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RobinSky
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I just some how fell into a wiki article about http://en.wikipedia.org/wiki/Insulator_%28electrical%29" and then read the following statement:

A true insulator is a material that does not respond to an electric field and completely resists the flow of electric charge. In practice, however, perfect insulators do not exist.

The question is, why is it that there are no perfect insulators? I thought things like plast, wood, didn't allow electricity to flow through at all, but of course physics does it again, turns your head completely upside down! :rolleyes:

Could anyone explain this? I tried to google it but didn't find anything relevant.
 
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For one thing valence electrons eventually break loose at high enough voltages...that is, the medium becomes a conductor.

A simple example is how a spark plug or lightning ionizes air which is a pretty good insulator (it must be since I don't get shocked sitting here at my computer with 120 volt ac nearby!)

Check here for some interesting background:

http://en.wikipedia.org/wiki/Electrical_breakdown

Some interesting photographs...
 
Ahha! I had no idea, thanks for the reply! :)