Double Window Security-tinted Check Envelope, #10, Commercial Flap, Gummed Closure, 4.13 X 9.5, White, 500-boxQuality Park Double Window Envelopes display both sender and receiver addresses for mailing statements and invoices. These security envelopes have a reflex blue pattern that protects sensitive client information because it obscures the details of the contents, even when held up to light. Seam Type: Diagonal; Flap Type: Commercial; Trade Size: #10; Security Tinted: Yes.