I think King Air windows (PAX) work off polaroid... two films, and the inner one can be spun around so it blocks out the light.
If you have 2 sheets of polaroid, if they are rotated to the right angle, there's no effect, but keep spinning them and it blocks out nearly all light (and visibilty) through it.
Personally I'd stay away from polarised if I was buying aviation specific glasses, because of the chance it could block out my GPS, or later a EHSI or similar
Get a nice pair of Ray Bans or Serengetis instead
Arrr!