500 6x9 WHITE POLY MAILERS ENVELOPES BAGS 6 x 9 By ValueMailers High Quality Self Sealing Mailers. Water, Tear and Puncture resistant. USPS, UPS, FedEx and DHL approved. The dark inner layer provides confidentiality and makes the mailer opaque. Pressure sensitive adhesive provides a high strength durable closure, water and dirt resistant High-efficiency mailers are perfect for shipping a wide variety of non-fragile items.