Electrical conduction is the movement of electrons through a material, creating an electric current. Some materials are naturally able to allow the flow of electrons through them, and we call these materials electrical conductors. Metals are especially good conductors of electricity. However, in order to make a conducting ink, you need a liquid, and most metals are solid at room temperature. To get around this challenge, the inventors of conducting ink used metal nanoparticles.

These nanoparticles are tiny spheres of metal, so small that you could fit over 5 million in the period at the end of a sentence. Each nanoparticle can conduct electricity, and when strings of nanoparticles form, like pearls in a necklace, electrons can travel from one nanoparticle to the next.

So, conducting ink usually contains two main components: metal nanoparticles (usually silver), and liquid to carry the nanoparticles. When you apply the mixture of liquid and nanoparticles to paper, it dries, and the random networks of nanoparticles that contact each other are locked in place. These networks of metal allow the ink to conduct electricity. You just laid down a path of silver for the electrons to follow.

It is unlikely, though, that this method of creating electrical circuits will replace the current method of producing circuit boards. The conducting ink relies on the random creation of paths of metal nanoparticles, so thicker films of ink increase the probability that enough paths of nanoparticles will form for sufficient electrical conduction. Current microchip fabrication involves creating circuits which are much smaller than the thickness of conducting ink you would need for the circuit board to work.

In the end, conductive ink works because it contains materials that conduct, most commonly silver. This material is usually dispersed throughout the ink as flakes or powder.

There are already some simple circuit boards made using conductive inks. For example, some subway and train systems use them to print circuits onto disposable passes. But the downside to conductive ink circuits is their resistance. Solid, pure metal will always be more conductive than the flakes or powder in conductive ink, so solid copper circuits will be more efficient with electrical energy and generate less heat.