Number 9 window envelopes are one of the most popular envelopes used in business. They are commonly referred to as a business reply or return envelope. A #9 envelope fits easily into a #10 envelope making it perfect for when you intend on someone sending something back to you. The window in this #9 reply allows the address of the recipient to show through. These envelopes can be completely customized with your logo and return address if you choose to use them as a smaller business envelope.
Tinted or security tinted envelopes have printing on the inside of the envelope to help eliminate the ability of someone to see what you are sending without opening the mail piece. Are you mailing sensitive information? If so, you will want to consider adding the security tinted option to your #9 envelope order.