Conservation Grade Super Acid-free Backings- Our .040" thick board is off-white, 100% alpha-cellulose board and buffered with calcium carbonate, which keeps the board from breaking down (indefinitely). It is acid-free (alkaline 8.0-9.0), lignin-free/contaminant-free. Suitable for conservation. Our material meets the Library of Congress Archival Standards. Acid-free board can trap migrating acids in paper and neutralize it. A buffered board can stop migrating acids from entering an object and therefore prevent damage.