Herein, we investigate the electrochromic performances in the infrared (I R) region, in particular in the midwavelength (MW, 3-5 mu m) and long wavelength (LW, 8-12 mu m) bands, of WO3 thin films grown by RF-sputtering and pulsed laser deposition. For an optimized voltage window, 200 nm room temperature thin films are the most efficient in the MW band, with the highest contrast in reflection, namely 35%, whereas thicker films, typically 500 nm, are required in the LW band. At 400 degrees C films show contrasts in reflection lower than 10%, surprisingly associated with a reasonable insertion amount of 0.20. Indeed, no straight correlation between the electrochemical and the optical properties in the I R region was established. (c) 2007 Elsevier B.V. All rights reserved.