The most economical way to package non-fragile items ClearBags® CoEx mailers, or poly mailers as they are sometimes called, are the most ideal way to package non-fragile items. They are made of a 3-layer co-extruded LDPE material that is opaque white on the exterior and light grey on the interior. Bags are lightweight to save on shipping costs. These 2.5 MIL mailers feature a permanent adhesive strip on the flap that makes the bags tamper proof. The strong side seams allow for overstuffing or bulky items without fear of tearing. Water Resistant. Labels adhere easily and the material is marker and pen friendly.