Quality Park - QUA90120 No. 10 window envelopes are essential for your business. They are made of 24 lb. white wove stock and perfect for invoices, checks, direct mail and more. 4-1/8" x 9-1/2" envelopes feature a moisture-seal commercial flap. Traditional diagonal seams are compatible with automated inserting and folding equipment. Window measures 1-1/8" x 4-1/2" and is positioned 7/8" from the left edge and 1/2" from the bottom.