The slide boxes hold 12, 25, 50 or 100 slides. They are made of of thickened ABS material and have numbered inserts. The 100 slide box has a metal closure latch. There are 2 types of slides mailers, the flat type that holds either 1, 2 or 3 slides, and the square type that holds 5 slides. They are made of clear polypropylene.