To build the speakers and the microphone, which are thinner than a temporary tattoo, the researchers needed to design electronics flexible enough to stretch and bend with the skin, without losing their capacity to conduct electricity and heat—both necessary to transmit audio signals.

After testing different materials, the scientists settled on grids of tiny silver wires coated with polymer layers, which were stretchy, transparent, and capable of conducting sound signals.

After receiving an electric audio signal from a music player, the tiny loudspeaker heats up the wire grid to about 33°C, which replicates the sound pattern by changing the pressure of the surrounding air. Our ears pick up these changes in air pressure as sound waves.