Quality Park® Window Envelopes are essential for your business. The reflex blue pattern protects sensitive client information because it s impossible to see the details of the contents even when held up to light. These 24-lb wove envelopes have traditional diagonal seams compatible with automated inserting and folding equipment. Each business envelope has a moisture seal commercial flap. Stock up on boxes so you don t run out! Security Tint & Address Window. Seam Type: Diagonal; Flap Type: Commercial; Trade Size: #10; Security Tinted: Yes.