Quality Park R2400 Advantage Flap Stik Tyvek Mailer, 9 x 12, White (Box of 100) Tyvek white security envelope with a 14-lb. paper stock features a self-seal Flap-Stik closure. Tamper Indicating Panel (TIP) incorporated into flapthe word OPENED appears in red to signal tampering. Tyvek envelope resists punctures, tears, and moisture. Lightweight envelope saves on postage. Flap-Stik self-sealing closure.