A poly mailer bag is a plastic sleeve that is made from polyethylene. The flexible material provides an added layer of protection against external weather conditions and is one of the more cost-effective solutions for shipping products. While you can purchase poly mailers bulk packs to save on the costs, these bags are also available in single packs for shipping a small number of goods. For any type of electronic component, you must use anti-static bags to prevent electric discharge from damaging the items.