A protector adapted to accommodate a transparency inserted therein in a moist state, the transparency drying out while in the protector and being thereafter maintained in clean, dust-free and dry condition so that it is useable with an overhead optical projector which casts the image carried by the transparency onto a viewing screen. The protector is constituted by an open-ended, rectangular sleeve formed of moisture-impermeable transparent synthetic plastic film material of high strength having front and rear panels between which the inserted transparency is sandwiched, and a sheet of hygroscopic transparent acetate film which is interposed between the moist transparency and the front panel. The sheet act to absorb moisture from the transparency and to dissipate it, thereby drying out the transparency.