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. Design features open-side style and convenient Flap-Stik closure. First-class envelopes made of DuPont Tyvek won't rip, tear or puncture. They are much stronger and more secure than traditional paper envelopes. These 14 lb. expansion envelopes are water-resistant and moisture-resistant. They are easy to use. Simply peel and seal.