E. Gerber Full-Back Silver/Golden Comic Size Acid-Free Backing Boards 7 1/2" x 10 1/2" Pack of 50 These are the highest quality boards found anywhere! At 42-Mil, these are twice as thick as regular backing boards! Made from 100% acid-free, virgin wood, cellular fiber, 42 mil. thick cardboard. Contains a 3% alkaline buffer and a pH content of 8.0-8.5. Sold in packs of 50; Measures 7 1/2" x 10 1/2".