Tyvek Booklet Expansion MailerExpandable Tyvek® mailer delivers the best possible protection at a shipping-cost-saving weight. Inserting and removing contents is easy because of its horizontal, open side orientation. Self-adhesive Flap-Stik® closure provides a secure, peel-and-press seal. Clean, crisp look makes a professional impression. Envelope Size: 12 x 16; Envelope/Mailer Type: Expansion Mailer; Closure: Self-Adhesive.