Partners Brand Expansion Poly Mailers are made from strong polyethylene and protect products from moisture during shipping. These mailers feature gusseted bottoms to allow for thicker items. They are puncture, moisture, tamper and tear resistant and feature an easy open perforated tear strip. High strength seams will keep contents intact even if over packed. Mailers measure 5" and are sold 100 per case. Strong polyethylene mailers. Protect products from moisture during shipping.outer and the inner lining is silver. Puncture, moisture, tamper and tear-resistant. High strength seams will keep contents intact even if over packed. Labels, ink and stamps adhere well. Opens easily with a perforated tear strip. Features gusseted bottoms to allow for thicker items such as binders, books and catalogs. Depth: 5". Expansion Poly Mailers feature gusseted sides for thicker items.