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. Seam Type: Center; Flap Type: Flip-Stik; Trade Size: #13 1/2; Security Tinted: No.