Polyjacket Poly Film Self Seal Mailer 12" x 15-1/2" Polyjacket poly mailers are designed with a bottom fold and strong side heat seals for uncompromisable bursting strength. Our Polyjacket poly mailers feature pressure sensitive self-seal adhesive closure system that is reliable, tamper-evident and super easy to use! Polyjacket poly mailers are the ideal solution in a wide variety of applications involving the shipment of clothing, soft goods, documents, parts, and pharmaceuticals, just to name a few.