Conventional loudspeakers produce sound by vibrating back and forth, but new speakers made from sheets of carbon nanotubes create music the way lightning generates thunder. When an audio-frequency electric current was applied to stretchable, flexible transparent films of 10-nanometer-thick carbon nanotubes, physicists at the Tsinghua-Foxconn Nanotechnology Research Center in Beijing unexpectedly discovered they could make sounds as loud as commercial speakers. The scientists reason that the electrified nanotubes heat and expand the air near them, producing sound waves. These loudspeaker membranes can be stretched up to twice their original length without breaking and with little change to sound intensity. These sheets could be placed over paintings, windows, video screens—even in clothing, the researchers say, as a means to keep a person warm. They even put their handiwork—described online October 29 in Nano Letters—on a waving flag.