Moisture- and rip-resistant mailer made of DuPont? Tyvek? delivers heavyweight protection. Expandable design is ideal for shipping bulky contents like books, binders and reports. Flap-Stik? closure provides a secure, peel-and-press seal. Envelope Size: 10 x 13; Envelope/Mailer Type: Expansion Mailer; Closure: Self-Adhesive; Trade Size: #97.