Quality Park® Survivor® 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. 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. USPS First Class Mail—Lightweight 14 lb Tyvek®. Seam Type: Center; Flap Type: Square; Trade Size: #13 1/2; Security Tinted: No.