All our Poly Bubble envelopes are 2.5 mil high quality tough, puncture, tear, and water resistant and quality bubble provides extra protection during transit. Use 4 x 7 white bubble envelopes with labels or why not just write on them if you want to save time and cost. Each 4x8 envelope mailer has a unique 2.5 mil thickness. As the sender all you have to do is peel off the self seal strip on the opening lip and fold over to make a permanent seal. Poly bubble mailers are perfect for fragile items, brochures, catalogs, books, bulky material, gifts, presents, electronic media and both Amazon and eBay. High quality self sealing bubble mailer envelopes, lightweight, which saves on postage fees.