OEM Quality Park Heavyweight Expansion Envelopes provide superior protection for mailing bulky items that are not too heavy. Made with heavyweight Tyvek, these envelopes are much stronger and more secure than traditional paper envelopes, ensuring they won't rip, tear, or puncture. Featuring an open-side style and convenient Flap-Stik closure, they are also water-resistant and moisture-resistant. Easy to use, simply peel and seal for a reliable mailing solution.