Made of pliable TPU with a conductive compound, these filaments produce wire, circuits, and other components that direct the flow of electricity in wearable and flexible devices, from watches to grippers. Combine them with an insulating material so the electricity flows only through the filament’s pathways and not the rest of the device. In addition to being flexible, TPU is also durable and handles stresses better than ABS and PLA.

Print these filaments on a fused filament fabrication (FFF) 3D printer. You don’t need a heated printer bed, and printed parts resist shrinking and warping as they cool. Because they’re flexible, these filaments print best at a slow, consistent rate; high print speeds could cause them to jam. They don’t stand up well to moisture, so store them in a dehumidifying cabinet or other sealed container with a desiccant to keep them dry.

To make sure your part conducts electricity properly, use an electrical resistance tester to measure the surface resistivity. The target surface resistivity for TPU is 10¹ to 10⁶ ohms. To adjust, change the temperature of your printer’s extruder. As the extruder’s temperature increases, so will the printed part’s conductivity.

Tensile strength is the best measure of a filament’s overall strength. Similar to the stress applied on a rope during a game of tug-of-war, it’s the amount of pulling force a material can handle before breaking. A higher rating means a stronger filament. A tensile strength of 5,000 psi and above is considered good; 12,000 psi and above is excellent.