Scientists Just Built The First Titanium Frame That Floats

Engineers Cracked the Code on Metal That Floats, Literally

A metal structure full of holes should sink the moment it touches water, by every normal rule of physics. Yet a team of engineers has built one that floats anyway, and keeps floating even after it’s been cracked, crushed, or torn apart. Published in the journal Advanced Materials, the study describes the first buoyant open-cell metal frame of its kind, a titanium mesh, called a lattice by engineers, that floats reliably in seawater and, for its weight, is stronger than common marine materials like stainless steel and high-density plastic.

Metal frames like this one, built from tiny repeating struts arranged like a microscopic jungle gym, already show up in airplane parts, medical implants, and military gear because they’re strong yet light. But there’s a catch when it comes to water: the same open structure that makes those frames useful also lets water rush in and drag the material to the bottom, no matter how light it looked on paper. Engineers at RMIT University in Australia, working with a colleague in France, fixed that by combining titanium with a foam filler in a way nobody had managed before.

Their solution: 3D-printed titanium struts that are hollow inside, like tiny pipes, injected with expanding polyurethane foam that seals the internal channels while leaving the outside open and porous. That detail matters, since the frame keeps the surface texture that makes it useful, while gaining just enough sealed-off buoyancy to float.

A New Density Formula Predicts Which Structures Will Float

Floating comes down to a simple idea: an object floats if its overall density, including any water that seeps inside it, stays lower than the density of the surrounding liquid. Engineers used to rely on bulk density to predict whether a material would float, but that number changes as water works into a porous structure over time. A frame like this one might seem light enough to float in the lab, then slowly take on water and sink as air pockets fill up.

Their fix was a new measurement called skeletal density, which counts only the metal shell and any sealed-off filler inside it, ignoring the open pores that would normally let water in. By designing the titanium struts to be hollow and sealing those channels with foam, the team could calculate ahead of time how light the sealed sections needed to be for the structure to float.

Tests in Freshwater and Seawater Confirmed the Prediction

Using a laser-based 3D printing process, the researchers built small titanium cube-shaped frames with hollow struts, then injected expanding polyurethane foam through the channels until it filled every passage and sealed itself off from the outside. They built versions with hollow channels from 2.5 to 4 millimeters wide inside each strut, deliberately designing some to float and others to sink, to test whether their density formula could reliably predict the outcome.

Each design was tested three times, submerged in fresh water and natural seawater from Port Phillip Bay, some for more than two months. Structures without foam sank every time, exactly as predicted, with air visibly bubbling out as water flooded their struts. The foam-filled versions built with a low enough sealed density floated with no leaking, closely matching the formula’s predictions, though the actual samples came out slightly denser than calculated. A separate two-week seawater soak confirmed the titanium resisted corrosion well, turning up barely any weight loss or strength drop.

The Structure Kept Floating Even After Cracking

Testing what happens after the material gets hurt produced the most surprising result. Researchers crushed foam-filled samples under a compression machine, pausing at several stages, from peak stress through the first cracks to a fully broken structure, and dunked each damaged sample back in water to check for buoyancy. Separate lab tests, compared against computer simulations, showed cracks consistently starting where the foam entered the struts. Even so, buoyancy held through every damage stage, failing only once compression got so severe that the sealed sections became denser than water. The foam stayed sealed and kept trapping air even as the metal cracked, acting like a built-in backup float, a real upgrade over a plain sealed metal frame, which would let water rush in the instant a crack formed.

A Stronger, Reusable Blueprint for Floating Metal

Structurally, the hybrid held its own too. Compared at matching densities, it outperformed high-density polyethylene and 316L stainless steel, two materials common in marine equipment, in strength for its weight, and adding the foam barely changed how strong or stiff the frame was versus the unfilled version. To show this wasn’t just a lab trick, the researchers built a small working buoy, about the size of a coffee mug, and tested it in real seawater under simulated turbulent flow. It floated steadily and rocked with the current, with no outer sealing or extra flotation aids.

What’s reusable here isn’t just one clever buoy but a formula other engineers could apply elsewhere. Because the approach only requires knowing a material’s basic density, the researchers say the same design principle could potentially adapt to other combinations, such as different metals paired with rubber, resin, or biodegradable materials for medical devices. That turns this project into a blueprint for buoyant metal structures built to survive real damage at sea.

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