Archival Methods Onyx 13x19" x 2" Portfolio Box, 13.75" x 19.5", Black Buckram / White Lining. Box core is Kappa binder's board (0.1), a bookmaking board with no glue between layers. Lined with 80 lb. acid- and lignin-free paper. PAT tested and passed. Covered in library quality F-Grade Buckram (poly-cotton) with a moisture-resistant, 100% aqueous acrylic coating. Adhesive is pH balanced and buffered, &lt;.0008% sulfur content