Protect your collectible BILLHEADS from dust, dirt, fingerprints and other airborne pollutants that cause the paper to breakdown. Store them in high-clarity, 100% virgin, acid-free polyethylene. Our poly bags hold size and thickness and have passed the Photo Activity Test (P.A.T.) which certifies that they are safe for long-term storage. For extra stiffness and to protect the edges and corners of the billheads, place a backing behind it, preferably an acid-free one. Acid-free backings neutralize acids that might otherwise cause the breakdown of paper.