Polypropylene Sheet Protectors... Pina Zangaro"s 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.Available in many standard formats to fit Pina Zangaro portfolio books and those from most other major manufacturers. These sheet protectors feature superior scratch resistance to make your work look better longer, a non-stick finish to prevent adhesion to your artwork and a thick liner sheet to support thin or fragile artwork.All formats are top-loading. Made of inert, unplasticized, heat resistant and chemically stable archival quality, heavy-duty .0045 polypropylene. Lined with 10 pt. black acid-free and lignen-free paper. Both plastic and paper pass the Photographic Activity Test (PAT) and meet all ANSI requirements for archival storage. Packed in tens in a protective metallic, resealable bag.