Our 18" x 20" Open Top Static Shielding Bags are made of a multi-layer laminated film which has a metal layer as its core. This 3 Mil static shield bag has a layer that functions as a barrier to electrostatic discharge or ESD which allows a charge to move around and not through the bag. The inner layer of this 18 inch static control bag provides static dissipative protection for the metal layer and also strengthens seal. The outer layer of this 3 Mil bag is a non-static generating layer that resists abrasion and puncture.