EcoSwift Brand 9 x 12 inch 1.7 mil Poly Mailers with self-sealing, peel and stick adhesive, keep contents secure and tamper proof. EcoSwift Poly Mailers are extremely durable and lightweight to help save you money on postage. Superior tear and puncture resistance. High strength seams for maximum protection. Silver lining inside keeps contents hidden from view. Surface easily accepts ink, stamps, and labels. Approved by shipping carriers.