Approved by U.S. Postal Service, Transit Sacs are sent through the mail or are used by messenger services. Choose from Flat or Expandable style. Zipper closure keeps mail intact. Contents are kept confidential by looping security seal through grommet and zipper pull. I.D. window and address card route sac. One-color imprinting available in upper left corner for an additional charge. Clear transit sac keeps contents in clear view, providing instant identification of contents. Made of rigid yet flexible 16-gauge vinyl. Flat transit sac style.