OEM Quality Park Lightweight Expansion Envelope, sold in a carton of 100. These regular-weight envelopes provide superior protection for mailing bulky items that are not too heavy. Made from DuPont Tyvek, they resist ripping, tearing, and puncturing, making them much stronger than traditional paper envelopes. The open-side style and convenient Flap-Stik closure ensure ease of use, while their water-resistant and moisture-resistant properties add an extra layer of security.