Archival Polyester (Mylar D is a trademarked polyester material that is no longer manufactured by DuPont). Polyester is an inert material of the highest purity and clarity. Our polyester film is approved by The Library of Congress for the indefinite storage of paper products (hundreds of years). Polyester (Mylar) will not discolor, damage or adhere to items placed inside it. It is a sturdy film that will give extra support to fragile documents. We use DuPont inert Melinex® or a suitable equivalent