Today I Learned#1

Polaroids are actually polarized crystals that are long and cylindrical, and through a chemical reaction are forced to align themselves in straight lines at a tilted angle.
Basically they are like venetian blinds and a thin film is coated onto surfaces, e.g. sunglasses, possibly diagonally and in a way that it allows for a clear viewing angle but no direct sunlight.

None of this is taken from the Internet and is just an explanation given by my well of knowledge aka Dad.