Pina Zangaros classic welded polypropylene sheet protectors have become the industry standard for high quality archival preservation and presentation of artwork and documents. The weld parallel to the binding edge acts as a hinge, allowing the sheets to lie perfectly flat, making these sheets ideal for use in screwpost books. They have no liner sheet and are punched only for use in screwpost books and 3-ring binders. These sheets have passed the Photographic Activity Test (PAT) and meets all ANSI requirements for archival storage. Packed in a protective metallic, resealable bag.