Widely used for Business and Personal correspondence
are commonly referred to as Courtesy Reply Mail (CRM), Business Reply Mail (BRM), or return envelopes.
#9 Standard Window
are one of the most popular commercial-sized window envelopes available, commonly used as a reply envelope for invoice and business mailings, sent to recipients inside #10 Envelopes in order to mail something back to the sender.
have a standard size of 4 1/8 inches high by 9 1/2 inches long. They're designed to hold a standard 8 1/2 x 11-inch piece of paper folded into three sections, making them practical for office use. They're perfect for sending invoices, checks, official correspondence, and other business letters.
#10 Standard Window
Perfect to mail monthly statements, monthly bills, and utility bills (commonly referred to as “transactional” mail) are frequently mailed in number 10 envelopes. Direct mail and policy renewals from insurance companies will often use a #10 as well.