Half-Back Acid-Free Backing Boards are made from 100% acid-free, 24-mil thick cardboard to ensure extra rigidity and protection; Produced with a 3% alkaline buffer throughout and maintains a pH content of 8.0-8.5 to further ensure the preservation of your collectibles; Meets strict U.S. Government standards for archival storage; Designed for use with E. Gerber Comic Book Archival Mylar Supply Products; sold in packs of 100. Measures 7 x 10 1/2