Titanium doesn't float. It's roughly 4.5 times denser than water, which is why every ship hull, submarine frame, and dockside piling made of the stuff relies on trapped air or buoyant hull geometry to stay up rather than on the metal itself. Researchers at RMIT University say they've broken that rule, 3D printing a titanium lattice structure with a density under one-tenth that of water — light enough to float on its own — while still coming in 70% stronger than stainless steel or HDPE at equivalent density. The team floated a printed marine buoy made from the material for two weeks in Melbourne's Port Phillip Bay and measured just 0.15% mass loss afterward, with under 1% strength degradation.
The result, published in Advanced Materials (DOI 10.1002/adma.74641), comes out of RMIT's Centre for Additive Manufacturing, led by Dr Jordan Noronha with project leader Distinguished Professor Ma Qian and co-authors Andrey Molotnikov, Milan Brandt, and Martin Leary. It's the kind of result that sounds like a press-release exaggeration until you look at the mechanism, which turns out to be fairly straightforward lattice engineering rather than some exotic new alloy.
How a Metal Denser Than Water Floats
The trick isn't the titanium itself — it's what the printer leaves out. RMIT's structure is built from a network of hollow, interconnected struts, printed so that each strut encloses a sealed void rather than a solid metal cross-section. According to VoxelMatters' report on the work, those hollow struts are filled with polyurethane foam, which traps gas inside the lattice and blocks water from migrating into the voids over time. Noronha describes the mechanism directly: tiny, sealed cells in the foam trap gas and prevent water from flooding the hollow struts. That sealing is what let RMIT validate sustained buoyancy in fresh water first — samples floated for more than two months — before the team moved to the harsher seawater trial. Anyone who has printed lattice infill in a slicer will recognize the basic geometry instinct here — trade solid volume for a truss of thin members to cut mass while keeping load paths intact — but doing it in titanium via metal additive manufacturing, then backfilling the resulting internal cavities with foam, is a manufacturing sequence that isn't practical with subtractive methods. You can't machine a sealed, interconnected internal void network into a solid titanium billet; you have to grow it, void by void, the way a powder-bed or wire-arc metal printer does.
The stainless-steel and HDPE comparisons in RMIT's release are worth sitting with. Stainless is the default material for a lot of marine hardware precisely because it resists corrosion reasonably well, and HDPE is the default for anything that needs to float cheaply — mooring buoys, floating docks, aquaculture infrastructure. RMIT's claim is that at matched density, the titanium lattice beats both by 70% on strength. If that holds up under independent testing at scale, it reframes the buoyant-structure design space: instead of choosing between a strong material that sinks and a light material that's comparatively weak, you'd have a metal lattice that does both.
The Seawater Test
Freshwater buoyancy is one thing; the ocean is a different environment entirely. Seawater carries dissolved salts that accelerate corrosion in most metals, plus biofouling organisms, wave loading, and UV exposure at the surface. Titanium's native oxide layer already gives it excellent baseline corrosion resistance — it's why titanium fasteners and dive gear show up in marine contexts — but a lattice structure has vastly more surface area exposed to the water than a solid part of the same mass, which is exactly the geometry that should make corrosion and water ingress worse, not better. RMIT's two-week Port Phillip Bay deployment was a direct test of that risk, and the numbers reported are small: 0.15% mass loss, under 1% strength loss. Two weeks isn't a multi-year service life, and RMIT's release doesn't report longer marine soak data yet, but as a first real-world exposure test the results suggest the foam-filled sealing strategy is doing its job rather than just working in a lab tank. The team also demonstrated the technology with a 3D-printed marine buoy that stayed stable in a turbulent seawater tank rotated up to 45 degrees — without a sealed casing, a protective coating, or any added flotation. That last detail matters: a lot of buoyant structures achieve flotation by wrapping a strong-but-dense frame in a separate airtight shell, which is itself a failure point if the shell is punctured. RMIT's lattice is reportedly buoyant and structural in the same part, with no secondary enclosure required.
What It Means for Makers
None of this is desktop-printable today. RMIT's structures come out of metal additive manufacturing equipment — likely powder-bed laser fusion, standard for research-grade titanium lattices, though the release doesn't specify the exact process — plus a foam-infiltration step, both well outside FDM or resin territory. So don't expect a titanium-lattice buoy on Printables next month. What's more interesting for makers to track is the pattern, not the material. Project leader Ma Qian has said that by swapping in a different fill material inside the same titanium framework, the team believes the approach could be tailored toward other applications beyond marine buoyancy — energy absorption, thermal management, and vibration control among them. Those are stated as potential future directions rather than demonstrated results, but the underlying idea is the same one behind this buoyancy result: "print a lattice shell, then fill the internal void with a second material" is a viable general-purpose technique for combining properties that don't naturally coexist in one material — light and strong, buoyant and rigid, hollow and damped. Multi-material and hollow-infill printing on consumer machines is already headed in this direction with things like gyroid infill and dissolvable-support cavities; RMIT's work is a data point for how far that idea scales when the base material is titanium instead of PLA. For anyone building marine hardware — floating sensor platforms, jetty components, aquaculture buoys — the practical near-term takeaway is to watch for this technique moving from research lab to production metal-printing service bureaus, the same way exotic lattice geometries did over the past several years once the CAD tools and print processes matured enough to make them orderable rather than experimental.
