Electrochemical impedance spectroscopy (EIS) was used to investigate 55% Al-Zn coated with different thin polymer coatings (= 1 um) containing a passivating inhibitor (CrfVIl) after exposure to a sodium chloride (NaCl) solution for variable times. Impedance data were analyzed using a model developed previously. Investigation of the effects oj polymer layer thickness, chromate concentrations, and polymer particle dimensions revealed the different aspects of the protective principle ojthis new type oj thin-film coating on 55% Al-Zn-coated sheet steel. Evolution of the coating behavior over time was studied in depth. © 1999, NACE International.