OEM Quality Park open-end expansion envelopes, sold in a carton of 100. These envelopes are made with heavyweight Tyvek, providing superior protection for mailing bulky items without the weight of traditional boxes. Designed with an open-end style and convenient Flap-Stik closure, they are much stronger and more secure than paper envelopes. Water-resistant and moisture-resistant, these envelopes are easy to use - simply peel and seal.