Full-Back Magazine Backing Boards 8 5/8" x 11 1/2" 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 8 5/8" x 11 1/2".