No. 9 Double Window Envelopes display both sender and receiver addresses to mail statements and invoices. Reflex blue pattern protects sensitive client information by obscuring the details of the contents even when held up to light. 24 lb. white wove envelopes feature side seams for a clean, professional look. Gummed flap requires moisture. 3-7/8" x 8-7/8" envelopes include a top window that measures 1-3/16" x 3-1/2" and is positioned 3/8" from the left and 2" from the bottom. Bottom window measures 1" x 4" and is 3/8" from the left and 1/2" from the bottom.