Liquid Metal 3D Printing That Steers Heat in Silicone

Liquid metal 3D printing reached a maker audience on September 28, 2026, when Virginia Tech graduate student Hugh Grennan printed a gallium-indium silicone that can steer heat. Tom’s Hardware reported a syringe-fed machine that stretches droplets inside the toolpath so heat runs along their length, from a source toward a sink. The same mix can also form a simple electrical trace that survives a cut. The conductivity numbers come from the lab’s papers, not from the video alone.

What's Happening

Tom’s Hardware’s September 28 report follows a segment on Joel Telling’s 3D Printing Nerd channel. Grennan mixed eutectic gallium-indium into uncured polydimethylsiloxane. He described the alloy as about three parts gallium and one part indium, liquid at room temperature. Shear breaks the metal into droplets on the order of 10 to 100 microns, each wrapped in a thin gallium oxide skin. About an hour in an oven turns the silicone from a gel into a solid. The droplets inside stay liquid.

The electrical demo used a cast slab, not the printer. Grennan pressed a line with an indenter until droplets merged into a track and a small LED lit. He cut across it with a razor, pressed again near the cut, and the LED returned, faintly. He said cutting does not necessarily raise resistance, because the liquid metal flows and reforms pathways. Before that press, droplets are insulated by silicone and by their oxide skins.

The print itself is about heat. The printer is a syringe machine the lab built so it can load the composite and extrude straight from the syringe. Droplet shape comes from the ratio of how fast the paste leaves the nozzle to how fast the bed moves. The right ratio stretches round droplets into long, thin ones. Grennan said heat then travels along the long axis, “away from a heat source to a heat sink.” Asked about uses, he pointed to custom heat sinks and stretchable wearable devices. Tom’s Hardware ties the “about 40 times” headline to a 2025 Advanced Functional Materials paper co-authored by Michael Bartlett: 9.9 W/m·K along the droplet direction, against 0.24 W/m·K for the unfilled elastomer in that study. The video did not produce that measurement.

Why Liquid Metal 3D Printing Matters on a Workbench

Most desktop printers move heat by accident. A hotend, a heated bed, and a part cooling fan are there to make plastic behave. This composite is the opposite job: the print is the thermal path. If you can lay a soft trace that dumps heat one direction and stays flexible, you get a different class of bench project — a wearable patch, a robot skin, a cover that needs to bend and still pull heat off a chip.

The electrical half is easier to copy in your head and harder to copy in a garage. Pressing droplets until they connect is a lab trick with an indenter, a microscope, and a known alloy. It is not a slicer setting. A maker watching the video should leave with the mechanism, not a shopping list: oxide-skinned droplets stay apart until force joins them, and liquid metal can flow back across a cut. That is why the LED returned. It is also why you should not assume a hobby paste mix will be safe, stable, or even the same alloy.

The Virginia Tech step is programming where the droplets point, so the soft part has a direction. Direction is the part a filament user cannot get from a tube of paste. Tom’s Hardware notes that some PC coolers already use a gallium alloy instead of thermal paste. That is a spread-on-the-die product, not a printed path.

How Liquid Metal 3D Printing Differs From Filament Printing

Keep the video, the printed composite, and the older stretch study in separate columns. Mixing them is how a 40-times headline gets applied to a demo that did not measure it.

What you saw or can read	What was actually shown	What it does not show
Cast slab on the video	A pressed line lit an LED and conducted again, faintly, after a razor cut and a second press	A thermal-conductivity number
Syringe print on the video	Bed-speed versus flow stretches droplets so heat is meant to follow the toolpath	A home filament profile, or a cure schedule for your oven
Hur, Markvicka, and Bartlett, 2025	Direct-ink writing set droplet aspect ratio and direction; conductivity along the long axis was 9.9 W/m·K, about 40 times the unfilled elastomer at 0.24 W/m·K	A result measured during the YouTube segment
Bartlett and colleagues, 2017	Stretching a liquid-metal elastomer raised conductivity to 4.7 W/m·K in a programmed stress-free state and 9.8 W/m·K at 400% strain	A printed, spatially varying heat map

What the Research Says

Hur, Markvicka, and Bartlett used direct ink writing to set liquid-metal droplet shape and direction inside a soft film, including different orientations in different places on the same sheet. Along the long axis of the elongated droplets, thermal conductivity reached 9.9 W/m·K, about 40 times the unfilled elastomer at 0.24 W/m·K. Infrared images of a high-power LED on the film showed heat leaving along the programmed path (Hur et al., 2025). That measurement, not the video, is what the headline is citing.

Bartlett, Kazem, Powell-Palm, Huang, Sun, Malen, and Majidi had already shown why droplet shape matters. In a soft silicone filled with eutectic gallium-indium, stretching the droplets raised thermal conductivity to 4.7 ± 0.2 W/m·K in a programmed, unloaded state and to 9.8 ± 0.8 W/m·K at 400% strain, from a base near 0.20 W/m·K. The composite stayed soft: modulus 89 ± 2 kPa after 200% prestrain, and a strain limit above 600% (Bartlett et al., 2017). Elongation creates the thermal path. Direct ink writing draws that path in a chosen direction without stretching the whole finished part. Neither paper is a consumer product test.

Frequently Asked Questions

What is liquid metal 3D printing with gallium and indium?

In the September 28, 2026 Tom’s Hardware report, Virginia Tech’s Hugh Grennan mixed room-temperature gallium-indium into uncured silicone and printed it from a syringe. Nozzle speed versus bed speed stretches the droplets so heat travels along their length. A lab paper, not the video, measured 9.9 watts per meter-kelvin along that direction.

Can I run this liquid metal silicone on a regular filament printer?

No. Grennan’s machine is a syringe printer built to push uncured composite, then an oven cures the silicone while the metal droplets stay liquid. A desktop filament printer melts a solid spool through a hot nozzle. The paste, the oxide skin on each droplet, and the cure step do not map onto a PLA profile.

Does a liquid metal silicone print replace a strong plastic part?

It solves a different problem. The Virginia Tech work is a soft composite that can steer heat and, when droplets are forced together, carry a simple electrical trace. It is not a rigid bracket. If the part must hold a load you can name, you still choose a structural material and a process meant for that load.

Fibricate's Place in This Story

A syringe-printed silicone answers “which way should this soft part send heat?” It does not answer “will this bracket hold?” Companies like Fibricate, whose FibreSeeker 3 continuous carbon fiber 3D printer co-extrudes thermoplastic with continuous tow from stock such as the continuous carbon fiber spool, sit on the load-bearing side of that split. Use a liquid-metal elastomer when the job is a flexible thermal or electrical path. Use continuous fiber when the printed path has to carry a force you can name. Fibricate does not sell gallium-indium paste, and a fiber printer is not a syringe machine for uncured silicone.

What to Watch Next

Watch whether the Bartlett lab publishes a printable feedstock with a stated cure schedule, droplet size, and conductivity that a second lab can repeat. Watch how often maker videos separate the electrical party trick from the thermal measurement. Tom’s Hardware also points at directed cooling for electric vehicles, robots, and electronics as named applications in the papers, which is a longer road than a YouTube slab. Over the next two years the useful split for a workbench is simple: soft, directional heat paths will keep coming out of syringe and ink-writing labs, while rigid parts that have to hold will keep depending on fiber, metal, or a tested engineering polymer.

References & Further Reading

1. Hur, O., Markvicka, E. J., & Bartlett, M. D. (2025). Anisotropic and Heterogeneous Thermal Conductivity in Programmed Liquid Metal Composites Through Direct Ink Writing. Advanced Functional Materials.
2. Bartlett, M. D., Kazem, N., Powell-Palm, M. J., Huang, X., Sun, W., Malen, J. A., & Majidi, C. (2017). High thermal conductivity in soft elastomers with elongated liquid metal inclusions. Proceedings of the National Academy of Sciences.
3. Virginia Tech lab 3D prints a liquid metal composite to guide heat. Tom's Hardware. Retrieved September 28, 2026.