theyve only been projecting through stuff for about 100 years now..
in order to keep the film viewing area in a theatre quiet theres usually a window (glass) that is projected through, keeping the projection room noise away from the patrons.
i dont see why plexi would be markedly different from regular flat glass.
if the projection lens sticks out far enough.. it may be possible to cut a hole in the plexi and use a glass UV/Protection filter on the projection lens.. but i doubt thatd be needed.
