Full-Backs offer the extra rigidity you need for those irreplaceable comics!These are the highest quality boards found anywhere! The boards are made from 100% acid-free, virgin wood, cellular fiber, 42 mil. thick cardboard; contain 3% alkaline buffer and a pH content of 8.0-8.5; are twice as thick as regular backing boards; and sold in packs of 50. Measures 7 5/8 x 10 1/2