Family Life What is a double window envelope? What is a double window envelope? Two-window envelopes display the return and mailing address. Self-adhesive envelopes feature a security-tinted inside for privacy and confidentiality. Moisture seal keeps contents secure. Related Posts:Can you print directly on an envelope?What is a #7 envelope?What is the difference between a catalog envelope and a booklet envelope?Is it better to use tinted moisturizer or foundation?