These Clamshell Photo Storage Boxes are made from 60 point archival boxboard. The material is acid-free, lignin-free, scuff-resistant board. It is buffered with 3% calcium carbonate, which blocks migrating acids. The interior is lined with a white paper which measures a pH of about 8.5. The boxes have metal-edged corners for stacking strength and are shipped assembled. They have passed the Photo Activity Test which means they are approved for long-term storage. Boxes are available in either blue-gray or black.