Nickel oxide (NiOx) thin films were deposited by direct current magnetron sputtering technique onto flexible substrates with various oxygen (O-2) partial pressures. The influence of O-2 contents during deposition process on film structure, morphology, composition, optical and electrochromic (EC) characteristics of the films were investigated. The EC response for nonstoichiometric NiOx films shows a strong dependence on grain size variations and surface morphology. Finally, the multiple-layer stacks ITO/NiOx/Ta2O5:H/WO3/ITO were sequentially vacuum deposited over flexible polyethylene terephthalate plates based on the optimization of NiOx single layers. A large optical contrast up to 60% and a good durability are obtained for full device. To perform preliminary research on the mechanical properties within flexible devices, we introduced nontrivial changes to the interfacial properties by replacing the glass with flexible polymers. The effects were studied through static bending and the nano-scratch test. (C) 2016 Elsevier B.V. All rights reserved.