New, wide band. flexible electrochromic displays have been realized with microporous membranes metallized with gold that acts both as an electrode and a reflecting layer. A control of the relative contribution of specular and diffuse reflectance to the optical response of displays can be achieved by Varying the size of pores in the membrane. The active layer is a thin conducting polymer layer electrochemically deposited on the metallized membrane. Polydiphenylamine and poly(3,4-ethylenedioxythiophene), which show good electrochemical and optical properties, were used as active layers. These devices exhibit great contrast in the visible/near infrared (IR) spectral region with high reflectance in their reflecting state. IR reflectance measurements showed that swelling can induce reversible wide band contrast in mid-IR and far-IR. These results were correlated to morphological changes induced by ions movements in the polymer films by using EQCM measurements with fast simultaneous acquisition of frequency and impedance.