OEM Quality Park Tyvek Expansion First Class Envelope, designed for mailing bulky items securely. Made from durable DuPont Tyvek material, these envelopes resist ripping, tearing, and puncturing, offering a stronger alternative to traditional paper envelopes. The open-side style features a convenient Flap-Stik closure for easy sealing. With water and moisture resistance, these envelopes ensure your contents remain protected during transit.