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 Size: 8 1/2 x 12; Envelope/Mailer Type: Shipping; Closure: Self-Sealing Adhesive; Trade Size: #2.