The flat cardboard slide mailers securely hold slides with or without a cover-glass. They feature an inner finger groove for effortless slide removal along with a cover that opens for viewing. The flat surface area is ideal for labeling or writing any necessary information. They are light-weight and reusable to minimize cost. The 20-place cardboard slide holder contains a numerical index that corresponds to the inner slide compartments. The inside flaps are recessed so that there is no contact or contamination between the slides and the cover when closed. With a 360° hinge, the cover folds flat underneath to save space when the holder is in use.