Due to their relatively high electrocaloric activity and mechanical flexibility, relaxor ferroelectric terpolymers are being used in the fabrication of electrocaloric cooling and heating devices, in which the heat transfer is done by latent heat when a fluid condenses on (or evaporates from) their surface. This work focuses on improving the surface wettability of flexible polyimide foils, which have been utilized to encapsulate electrocaloric terpolymers for enhancing heat transfer efficiency. The polyimide foils were exposed to a combination of plasma etching and metal oxide thin film deposition using magnetron sputtering technology. With the aim of achieving a complete wetting surface, sputtering parameters such as pulse times, gas concentration and treatment time were varied. The chemical and physical properties of the treated surfaces were analyzed, and their influence on wetting performance was investigated at macro-, micro-, and nanoscale levels. The findings of this study have significant implications for the development of more efficient and reliable electrocaloric heat pumps, contributing to the advancement of environmentally friendly, energy-efficient solid-state cooling and heating technologies.