OEM Quality Park Open-End 1st Class Envelopes provide superior protection for mailing bulky items that are not too heavy. These envelopes serve as an ideal replacement for costly boxes or cartons. Featuring a convenient Flap-Stik closure, they require no moisture to seal - simply peel and seal. Made from DuPont Tyvek, these envelopes are much stronger and more secure than traditional paper envelopes, ensuring they won't rip, tear, or puncture. Additionally, they are water-resistant and moisture-resistant, with an open-end style for easy insertion.