Regular-weight Expansion Envelopes offer superior protection for mailing bulky items that are not too heavy. They are ideal replacements for costly boxes or cartons. Convenient Flap-Stik closure requires no moisture to seal. Simply peel and seal. Much stronger and more secure than traditional paper envelopes, these first-class envelopes are made of DuPont Tyvek and won't rip, tear or puncture. These 14 lb. expansion envelopes are also water-resistant and moisture-resistant. Open-end style offers easy insertion.