No. 10 envelopes feature two poly windows for the return and mailing addresses. The inside tint provides privacy for sensitive documents. These 24 lb. envelopes are compatible with most standard 8-1/2" x 11" computer-generated invoices and statements. The top window measures 3-1/2" wide x 1" high, positioned 1/2" from the left and 2-1/2" from the bottom of the envelope, while the bottom window measures 4" wide x 1-3/8" high, located 1/2" from the left and 3/4" from the bottom. Flaps are gummed for easy closure.