Regular-weight Expansion Envelopes offer superior protection for mailing bulky items which are not too heavy. Ideal replacement for costly box or carton. Offers open-side style and convenient Flap-Stik closure. Envelopes made of DuPont Tyvek won't rip, tear or puncture. Much stronger and more secure than traditional paper envelopes. Expansion Envelopes are water-resistant and moisture-resistant. Easy to use. Simply peel and seal.