Polypyrrole films were formed with hexacyano-ferrate (HCF) anions as exclusive dopants. It was observed that a portion of the built-in HCF displayed reversible electro-chemistry, but the majority of the doping anions are non-electroactive, while they are inside the polymers. Calculations showed that one excess positive charge on the polymer backbone was compensated by one HCF ion, thus, the entrapment of these multivalent anions was accompanied by the inclusion of a large amount of cations as well. These films were sensitive for the size of the cations present in the solution.