The antifungal substance polyhexamethyleneguanidine (PHMG) has been proven safe for paper and may be used for restoration of library materials of any value. PHMG is distributed evenly in paper and does not increase the moisture content. It is notable for its specific action on cellulose-deteriorating fungi and inhibits the activity of their cellulases. PHMG does not change paper durability but in combination with polyacrylamide and polyamidamine it increases paper permanence and resistance to wear. Treatment does affect the optical qualities of paper and PHMG is non-toxic. See also AATA 16-346.