1000 9" X 12" Poly Mailer Shipping Mailing Envelope Bag Low Cost 2.5 Mil Thick 1000 / Case Poly Mailers has Self-seal lip and tape provides quick and easy closure. Poly Mailers have Silver inner lining which provides confidentiality. Pressure Sensitive adhesive provides a high strength durable closure, water and dirt resistant. Pressure Sensitive Seal that is tamper evident and secure. Poly Mailers are available in variety of sizes which can be shipped today.