Imagine a window that switches quickly between clear and opaque to let in the morning sun and provide privacy when needed. Prototypes of such “smart glass,” often based on liquid-crystal technology, have been around for years, but they remain too expensive for wide use. Dutch researchers Peter G. Steeneken of NXP Semiconductors, Daan van den Ende of R&D firm TNO, and coworkers have demonstrated a new route to such materials by using an electric field to wrinkle low-cost transparent elastomers. The team sandwiched the polymer films between a clear electrode and a flexible thin film of gold. When they applied a voltage to the electrodes, an energetic instability induced in the elastomer layer caused the material to wrinkle microscopically, and the device went from mostly clear to translucent (Adv. Mater. 2013, DOI: 10.1002/adma.201300459). When the voltage was removed, the device became clear again. In addition to optical applications, the researchers say, the voltage-tunable roughness offered by the approach could be used to control wettability, friction, or aerodynamics.