Archival Methods' Museum Board is made of 100% cotton fiber. Bright White is a neutral tone board, is acid- and lignin-free, and incorporates alkaline or neutral sizing. All boards are buffered with calcium carbonate. This ensures protection from the destructive effects of acid migration from the matted work and from a polluted environment that might cause the pH of the mat board to decrease (become more acidic) with age. No optical brightening agents are used in the manufacture of Archival Methods' 100% Cotton Museum Board.