2 poly windows for the return and mailing address Security-tinted inside for privacy and confidentiality. Compatible with most standard computer generated invoices and statements. Made of crisp 24-lb white wove for a professional feel. Quality Park(R) Double-Window Security Envelopes, #10, 4 1/8in. x 9 1/2in., White, Box Of 500 is one of many Business Envelopes available through Office Depot. Made by Quality Park.