Virginia Tech’s Soft Materials and Structures Lab, run by mechanical engineering professor Michael Bartlett, has printed a silicone composite that hits 9.9 W/mK thermal conductivity along the direction of its embedded liquid metal droplets, about 40 times the conductivity of unfilled PDMS silicone. The number comes from a 2025 paper in Advanced Functional Materials co-authored by Bartlett.
The process, demonstrated by graduate student Hugh Grennan on the 3D Printing Nerd YouTube channel, mixes eutectic gallium-indium (roughly three parts gallium to one part indium, liquid at room temperature) into uncured PDMS. Mixing breaks the metal into droplets 10 to 100 microns across, each wrapped in a thin gallium oxide skin. An hour in an oven cures the silicone into a solid while the droplets stay liquid inside it. Printed from a syringe-fed machine, the ratio of extrusion speed to bed speed stretches the round droplets into long, thin ones, which is what lets heat travel along their axis toward a heat sink instead of scattering.
| Measurement | Value |
|---|---|
| Thermal conductivity (along droplets) | 9.9 W/mK |
| Improvement over unfilled silicone | ~40x |
| Droplet diameter | 10 to 100 microns |
| Cure time | about 1 hour |
The same material carries current when droplets are forced to merge, which Grennan showed by pressing a line into a cast slab hard enough to light an LED, then cutting the line with a razor blade. Pressing near the cut relit the LED, because the liquid metal simply flows around the break rather than staying severed, a mechanism the lab’s separate 2024 Additive Manufacturing paper attributes to the oxide skin’s role in keeping droplets in shape until they’re forced to reconnect. Bartlett’s group lists directed cooling for EVs, robots and electronics, plus stretchable wearables, as target uses, and has a newer paper on a stretchable liquid metal-polymer feedstock for self-conducting printed parts.