These OEM Quality Park Postage Saving Window Envelopes are designed to hold extra documents while providing value based on shape-based postage costs. By switching from a flat mailer to a letter-rate size, you can effectively reduce postage expenses. Made from white heavyweight paper, these envelopes feature an inside tint and a large flap with extra adhesive for secure mailing. Each box contains 500 envelopes, with a size of 6" x 9-1/2".