Quality constructed single window envelope. Pre-print with your return address to save time, ensure legibility and make a more professional impression.Our industry-best single window confidential mailing envelopes keep vital information safe and secure during mailing. Standard #10 envelopes accommodates same size business checks and correspondence.Protect your business from prying eyes and frauds: This #10 envelope is lined with blue tinted pattern so private information and numbers don't show through.