E. Gerber Full-Back Standard 42-Mil Comic Book Backing Boards 7" x 10-1/2" - Full CASE of 500 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. Boards Measure 7" x 10-1/2". Full Case of 10-Packs of 50 - 500 Total.