Vapor capsules contain a unique phase inhibitor designed to protect metallic surfaces within an enclosure against airborne corrosion. Simply place these self-contained capsules inside an enclosure, the vapors readily permeate every point, passivating all metallic surfaces. When the capsule is removed from its sealed package, it begins to emit an invisible, no-toxic vapor which is diffused throughout the surrounding atmosphere until the air is saturated. The vapor then passivates the metal surface against atmospheric corrosion by reducing the electrochemical activity of the metal surfaces.