This paper reports the fabrication of a high-speed polyimide capacitive relative humidity sensor with a multi-walled carbon nanotube (MWCNT) film network electrode, which is coated by the spray-deposition process. A spray-coated MWCNT film top electrode has high surface area, low resistivity, and interconnected open pore structure, which makes water molecules accessible to all polyimide surfaces. Capacitive humidity sensors with MWCNT film electrodes have three times faster adsorption and desorption times than porous metal electrode sensors. The much faster response times of MWCNT electrode sensors is attributed to the percolated pore network, which allows more water molecules to be accessible to polyimide surfaces. (c) 2013 Elsevier B.V. All rights reserved.