This 25 pack of Print File 35 6HB Negative Preservers holds six 35mm strips of 6 frames, 36 frames total and contact prints on 8-1/2" x 11". These sleeves feature exclusive thin backing coupled with high clarity, which allows you to make quality contact sheets without removing or handling negatives. They provide strong continuous seams prevent negative hang up. The top sheet is 3 mil and the bottom sheet is 1.8 mil. These Print File sleeves are archival quality polyethylene and safe for long term storage. PAT passed.