Double Window Security-tinted Check Envelope, #9, Commercial Flap, Gummed Closure, 3.88 X 8.88, 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: #9; Security Tinted: Yes.