Heavy-Duty Plastic Sleeves, Letter, Polypropylene, Clear, 12/Pack, Sold as 12 Each Heavy-duty polypropylene sleeves with see-through front are archival safe, sealed on two sides, thumb notched and letter sized. Reusable heavyweight sleeves are perfect for projects and organizing office space. Clear folder allows you to view contents easily. Sealed on two sides to hold items securely. Non-stick, polypropylene material won't lift print.