Squall

yeah, i don't know the name of it, but there is a piece of material, that if you hold two of them in one way, they block out some light, but if you turn one of them 90 degrees, it blocks out ALL light. last time i saw a 3d movie i got some of these in the glasses, and they're pretty cool. my physics teacher had a couple of these, and thats how i know about how they work!