Advanced materials with large and dynamic variation in thermal properties, sought,for urgent defense and space applications, have heretofore been elusive. Conducting polymers (CPs) have shown some intrinsic variation of mid- to far-infrared (IR) signature in this respect, but the practical utilization of this has remained elusive. We report herein the first significant IR electrochromism in any material, to our knowledge, in the 0.4 through 45 mum region. This is seen in practical CP devices in the form of thin (<0.5 mm), flexible, entirely solid-state, variable area (1 cm(2) to 1 m(2)) flat panels. Typical properties include: very high reflectance variation; switching times <2 s; clyclabilities of 10(5) cycles; emittance variation from 0.32 to 0.79; solar absorptance variation from 0.39 to 0.79; operating temperatures of -35 to +85degreesC; durability against gamma-radiation to 7.6 Mrad, vacumn to 10(6) torr, and simulated solar wind (e.g., 6.5 x 10(16) e/cm(2) @ 10 keV).