What is a VCI Bag? VCI Bag, or Vapor Corrosion Inhibitor bag, is a poly packaging film converted to a bag that is manufactured with added VCI chemistry. VCI molecules protect metals from corrosion by forming a thin, invisible layer on the surface. This layer inhibits the corrosion process caused by oxygen, water, and contaminants. A Vapor Corrosion Inhibitor bag can be made in different sizes, weights, seals, and inhibitor types. How do VCI Bags Work? VCI bags, or Vapor Corrosion Inhibitor bags emit molecules that settle on metal surfaces and form an invisible layer that protects from corrosion. It protects by interrupting the electrochemical corrosion process caused by moisture, oxygen, and contaminants in the atmosphere.