3M Non-Printed Zipper Closure Packing List Envelope NPZ-L is a 8.5" x 11.5" unprinted, clear polyethylene envelope with a zipper closure for easy and secure open and close. We designed this envelope with a high-tack rubber resin adhesive that sticks on contact to packages. Oil- and water-resistant, this packing list envelope securely protects documents from damage throughout delivery.