These are OEM Quality Park Survivor First Class Envelopes, designed for secure and reliable mailing. Featuring a patented release strip, these open-end catalog envelopes are easy to open. The convenient Flap-Stik closure does not require moisture to seal, ensuring a secure seal every time. Made from DuPont Tyvek, these envelopes are much stronger and more secure than traditional paper envelopes, making them resistant to ripping, tearing, or puncturing. Additionally, they are water-resistant and moisture-resistant, lightweight, and ideal for saving on postage costs.