OEM Quality Park Reveal-n-Seal double window envelopes come in a box of 500. These envelopes feature a unique adhesive that ensures a strong, moisture-free secure seal and an extended shelf life. The design includes an inside tint and perforations along the flap to reveal any tampering. No. 9 envelopes are compatible with most standard 8-1/2" x 11" invoices and statements, and are made from durable 24 lb paper.