Packzon Poly Mailers Envelopes Shipping Bags Premium Self Sealing 100 10x13 Bags with 2 in Flap Pack of 100 10" x 13" Poly mailer Envelopes Constructed from 2.5 mil three layer co-extruded polyethylene film, 2 inch flap with a self-seal closure on one end Three layer co-extruded polyolefin (polyethylene) film. Material is waterproof, seal is not. Material is waterproof, seal is not. Acid free PACKZON Brand 100% Satisfaction Guaranteed