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I was getting my filters mixed up. There is a UV filter you can adapt and [excessive UV light causes distortion… heres an in depth explanation](http://photo.stackexchange.com/questions/2262/are-digital-sensors-sensitive-to-uv)
The best way to describe polarizing filters though is that they remove sunlight that has reflected off surfaces, including water molecules such as clouds. Easiest way to see this is in pictures of water or metallic surfaces.
[Here’s a comparison of the sky](http://upload.wikimedia.org/wikipedia/commons/d/d8/CircularPolarizer.jpg)
[This is also how you get the “invisible water” look on still water](http://i.imgur.com/1LKAb.jpg?1). Water is only as visible to our eyes as the light that reflects off (wavelengths hit at too shallow of an angle to penetrate) of it since it’s naturally transparent.