Conveniently primed for immediate shipping, Ship-Lite® envelopes offer the insurance that special packages need. Fans of self-sealing envelopes will appreciate the Redi-Strip® adhesive and simple peel and seal release. At the post office, USPS's First Class Mail® deco is already printed on, which guarantees speedy delivery and damage control. As an extra precaution, each envelopes also features a water-resistant surface to fend off rainy weather. USPS First Class Mail. Seam Type: Center; Flap Type: Cheese Blade; Trade Size: #13 1/2; Security Tinted: No.