These 2 mil Comic Book Bags are made of Archival Polyester (Mylar) an inert material of the highest clarity. Mylar will not discolor, damage, or adhere to items placed inside it. It is a sturdy film that beautifully displays, timelessly protects and gives extra support to fragile documents. Resistance to moisture, insect attack, fungus, mold, mildew, acid, oils, grease, and solvents. Mylar contains no dangerous plasticizers, slip additives, surface coatings, antioxidants, acid-hydrolysis.