OEM Quality Park First Class Expansion Envelopes come in a carton of 100. These envelopes are made with heavyweight Tyvek, providing superior protection for mailing bulky items that are not too heavy. The open-side style and convenient Flap-Stik closure make them easy to use. Unlike traditional paper envelopes, these water-resistant and moisture-resistant envelopes won't rip, tear, or puncture, ensuring your items are secure during transit.