Expandable mailer made with DuPont™ Tyvek® material 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 Redi-Strip® closure provides a secure peel-and-press seal. Clean crisp look makes a professional impression. Heavyweight 18 lb Tyvek®. Seam Type: Center; Flap Type: Square; Trade Size: #15; Security Tinted: No.