Survivor R4510 Tyvek Expansion Mailer, First Class, 10 x 13 x 1 1/2, White (Case of 100) Tyvek white expansion envelope features a Flap-Stik self-adhesive closure. Use for bulky items. Resists punctures, tears and moisture. Expands on sides to fit binders, books, reports. Use instead of cartons or boxes.