From the manufacturer:
These self sealing art, print and photo bags make protecting artwork easy and worry-free. Artwork simply slips into a Krystal Seal bag which has a resealable flap, and is ready to store in a flat file, portfolio, print rack or storage box.
Krystal Seal Art Bags are great for storing prints, drawings, watercolors, matted and mounted artwork in a variety of sizes. These bags are archival, crystal clear and made of 2 mil Polypropylene. They provide a professional finish to presentations and are perfect for home, gallery and outdoor shows. Packages of 25.