A duplex coating is formed by painting or powder coating over hot dip galvanized steel. When used together, the corrosion protection provided by the galvanizing and painting/powder coating is far superior to either protection system used alone. Many products, such as automobiles and radio towers, have utilized duplex systems successfully for decades. How it works: In order to protect steel from corrosion, something must interfere with the corrosion cell, either by blocking the electrolyte (a medium for conducting ions: water) or by becoming an anode. Two common methods of corrosion protection are barrier protection (blocking the electrolyte from the steel surface) and cathodic protection (the formation of another anode). Hot dip galvanizing alone offers both types of protection; however, painting or powder coating over hot-dip galvanizing creates an additional barrier layer on top of the zinc coating.