These bags are usually plastic polyethylene terephthalate (PET) and have a distinctive color (silvery for metallised film, pink or black for polyethylene). The polyethylene variant may also take the form of foam or bubble wrap, either as sheets or bags. Because of the need for protection against mechanical damage as well as electrostatic damage, layers of protection are often used; because of this, a protected device can be packaged inside a metalized PET film bag, which is packed inside a pink polyethylene bubble-wrap bag, which is finally packed inside a rigid black polyethylene box lined with pink poly foam.
To create the anti-static effect, the black or silver bags are slightly conductive, forming a Faraday cage around the item to be protected and preventing any localized charges from being deposited onto the protected devices as the bags are handled. The pink or green bags are made of low-charging material, i.e., the bag itself will not create harmful charges, but will not protect the item from electric fields. It is important that the bags only be opened at static-free workstations.