#10 All Purpose Window Envelope The #10 envelope is a versatile size most commonly used to store letterhead size paper that is folded into thirds. Simply position both the return address and the recipient address to show through the envelope's large left side window, and you're good to go! Peel & Seal Closure This envelope is easily sealed via the Peel & Seal Closure along the back flap. Peel it. Seal it. Done! Easily Personalize by Using a Printer or Writing by Hand Compatible with most digital and offset printers, these envelopes are easy to customize. Want more of a DIY look? Gel Pens, Calligraphy and other hand crafts look amazing! LUXPaper is a premium stationery and office supplies brand focused on quality and variety. Our assortment of premium paper ranges from lightweight text stock to heavyweight cover stock, and every weight in between. LUXPaper products, including paper, cardstock, envelopes, and more, are available in a wide selection of sizes and in the largest variety of colors.