OEM Quality Park Heavyweight Expansion Envelopes, sold in a carton of 100. These envelopes are made with heavyweight Tyvek, providing superior protection for mailing bulky items. They feature an open-side style and a convenient Flap-Stik closure, ensuring secure sealing. The Tyvek material is resistant to ripping, tearing, and puncturing, making these envelopes much stronger than traditional paper options. They are also water-resistant and moisture-resistant, providing added durability for your mailing needs.