JAM Paper and Envelope s Heavy-Duty Tyvek Open End Catalog Envelopes are some of the strongest and sturdiest envelopes available. Composed of high-density polyethylene fibers that won t rip tear or puncture they feature an open end flap with self adhesive strip closures. Lightweight and water-resistant protecting documents from whatever your school home or office will throw its way. Use them for organizing or mailing important documents at school home the office or out on the go!