Barrier Bubble lining retains air better than alternative cushioning materials. Polypropylene exterior is moisture-, puncture- and rip-resistant. Co-extruded seams are heat-sealed and burst-proof. Self-seal closure features a tamper indicator. Envelope/Mailer Type: Cushioned/Media; Envelope Size: 4 x 8; Closure: Self-Adhesive; Trade Size: #000.