Essentially there are three categories of ESD bags: antistatic bags, dissipative bags and metallized bags.
Metallized shielding bags have either a metal film embedded into the bag film construction or coated onto an existing layer. This metal film acts as an electrical shield against electrical discharges from the outside of the bag. Depending on the energy and duration of the discharge and the thickness of the metal film, an ESD event is typically spread out over the outer surface of the metal film and if fully enclosed, i.e. the bag is sealed, then the charges current from the ESD event is contained to the outside (outer surface) of the metal film, i.e., providing a region of no electrostatic fields within the bag, thereby protecting the contents within. This effect is known as the Faraday Cage Effect and is commonly used in controlling ESD via metallized shielding bags, conductive bags and the conductive tote box with a cover.