These self-seal 15" x 20" + 4" Bottom Gusset Poly mailers are the perfect packaging material to protect your bulky apparel, bags, textbooks, or blankets from dirt and moisture during shipping and handling. Expansion poly mailers feature a 4" gusseted depth, which makes packing and shipping bulky items such as binders, books, jackets, and catalogs possible and convenient. Our expansion poly mailing envelopes have a peel-and-seal lip that provides a secure, tamper-evident closure and is the ultimate lightweight, low-cost shipping solution for bulky, non-fragile items. Custom Printing Available.