Half-Back Silver & Gold Comic Book Backing Boards 7 1/2" x 10 1/2" These are the highest quality boards found anywhere! At 24-Mil, these backing boards ensure extra rigidity and protection! Made from 100% acid-free, virgin wood, cellular fiber, 24 mil. thick cardboard. Contains a 3% alkaline buffer and a pH content of 8.0-8.5. Sold in packs of 100 and measures 7 1/2" x 10 1/2".