Quality Park Security Tint #10 Window Envelopes have a reflex blue pattern to protect sensitive information. This special tint prevents a security breach because the contents are not visible even when held up to light. Each moisture sealed envelope is made of 24 lb white wove paper with traditional diagonal seams that work with inserters and automated folding machines. Envelopes seal closed by simply adding moisture to the gummed, commercial flap. Available in boxes of 500 so you never run out! Envelope dimensions are 4 1/8 inches x 9 1/2 inches. Window dimesions are 4 1/2 inches x 1 1/8 inches, 7/8 inches from the left edge and 1/2 inch from the bottom.