Quality Park® Survivor® Tamper Evident Catalog Mailers are made with durable 14 lb DuPont™ Tyvek®, which is strong enough to withstand the most grueling conditions. The material is puncture, tear and moisture resistant—virtually indestructible. Yet, it is still lightweight which can provide a savings on shipping costs. Each envelope has a unique tamper indicating panel that displays the word "OPENED" in red if the seal is broken. These white mailing envelopes feature an easy Flap-Stik® closure which requires no moisture for a secure seal and a release strip for quick, easy opening. When sending critical documents, Survivor Tamper Evident Catalog Mailers are the safe, cost effective way to make sure your items get there intact. Tyvek® is a trademark of DuPont used under license by LSC Communications US, LLC d/b/a TOPS Products.