Featherweight, moisture and rip resistant TyvekŪ mailer delivers heavyweight protection. Expandable design is ideal for shipping bulky contents like books, binders and reports. Flap-StikŪ closure provides a secure, peel-and-press seal. Bright white appearance makes a professional impression. Stock up and save! Envelope Size: 10 x 13; Envelope/Mailer Type: Expansion Mailer; Closure: Self-Adhesive.