INK is an age-old medium, yet it’s keeping up with changing times. It’s long been used in pens, of course, and more recently in printer cartridges, but now it’s also being mixed to print lightweight circuits, sensors and switches.

Circuits made with conductive inks that can withstand the rigors of pressure, heat and moisture are replacing copper wire and bulky connections in many new products. The ink circuits, typically made with a range of conductive materials, are printed on surfaces like plastic, cloth and paper.

One company, T-Ink, has developed inks so robust that circuits, sensors and switches can be printed on flat plastic and then molded into three-dimensional components that control overhead lights and sunroofs in cars. The surface of the control panel is touch-sensitive, so just a tap can turn the lights on. And the process is potentially less costly than current methods.

“This is a highly imaginative use of printed electronics,” said Harry Igbenehi, a technology analyst who follows printed electronics at IDTechEx, a consulting company in Cambridge, England.