How do polarised 3D glasses work?

For linear polarisation the filters in the glasses are placed so that they are at perpendicular to one another. The polymer strands in the filters are arranged usually at 450 and 135o, and therefore only allowing the light polarised at those angles through to they eyes. This allows the wearer to see the different images designated to the left and right eye. Therefore producing the 3D effect.

However more modern 3D glasses will use circular polarisation, either clockwise or anticlockwise. This a more effective way as the image will not fade regardless of your heads orientation, the left will always see the image intended for it and vice versa.