2.5 Mil Quality Self Sealing Mailers, 3 layer co-extruded polyethylene film. Pressure sensitive adhesive provides a high strength durable closure, water and dirt resistant. High strength seams allow for over-stuffing. BLACK INTERIOR FOR SECURITY OF CONTENTS. TEAR AND RIP RESISTANT. High-efficiency mailers are perfect for shipping a wide variety of non-fragile items. These Envelopes exceed UPS, FEDEX and USPS regulations, and can be used for all of your packages!