Electrochemically deposited polypyrrole thin-film gas sensors have been observed to exhibit significantly different structural and morphological properties on variation of deposition conditions. The careful control of all deposition variables, therefore, is crucial if reproducibility is to be attained. This paper attempts to explain the origins of a novel morphological variant which involves the formation of a tendrillar texture on the growth face of the polymer thin film. We suggest that this morphological feature is the result of variations in electrolyte purity levels during electrochemical deposition. We show that the oxidation of pyrrole monomer is a significant source of electrolyte impurity.