A duplex coating is defined as a combination of two different coating systems that often complement one another, Typically this means a metallic coating overcoated by an organic system. Examples of such systems are hot-dip galvanizing surfaces that have been painted or powder-coated.

Typically, a galvanized coating on its own will provide adequate corrosion protection. However, organic may be applied over the galvanized finish for a number of reasons such as to add colour for improved aesthetics, to try to blend the structure into its surroundings, to try and make the structure stand out from its surroundings, or to provide additional corrosion protection in a very severe environment.