3D-Printed Plastic Struts Could Make Helmets Ten Times Safer

The needle goes in at an angle, pauses for roughly three seconds, and withdraws. Where it has been, a thin column of liquid elastomer sits inside the foam’s open pores, curing slowly in place. The whole sequence takes about as long as tying a shoelace. Then the printer’s gantry moves to the next position and does it again, and again, and again, building very methodically what its creators at Texas A&M University call a skeleton.

What they end up with is ordinary polyurethane foam transformed. The finished block looks unremarkable from the outside, perhaps slightly stiffer to the touch. But compress it hard and the difference becomes clear: it absorbs nearly ten times the energy of the foam it started as, at almost no additional weight, and then (unlike most high-performance energy absorbers) springs back, ready to do it again.

Mohammad Naraghi, who directs the Nanostructured Materials Lab at Texas A&M, has spent years thinking about the problem that sits at the heart of protective foam design. Engineers have long had two options, neither satisfying. Conventional foams are cheap to produce at scale but impossible to tune with any precision: their internal structure is chaotic, random, a product of the bubbling chemistry that makes them. Engineered lattice materials, by contrast, can be designed strut by strut for precise mechanical performance, but making them is slow, expensive, and hard to scale beyond laboratory samples. The Army, which funded Naraghi’s work, wanted something that combined the best of both.

The solution his team devised, working alongside Eric Wetzel of the DEVCOM Army Research Laboratory, was, in retrospect, the obvious thing nobody had tried. “IFAM is a simple, computer-driven manufacturing process that allows us to build an elastomeric skeleton inside of a conventional open-cell foam,” says Wetzel. The foam does the dual job of holding the injected resin in shape while it cures (no complicated mould required), and of becoming the permanent host matrix for the resulting struts.

Those struts are doing something more interesting than simply adding material. Under compression, the foam and struts cooperate in a way that neither could manage alone. At low loads, the surrounding foam acts as a brace, preventing the thin plastic columns from buckling prematurely. At higher loads, the struts push the force outward into the foam, spreading the load laterally. The net result is what the researchers call a synergy index well above two, meaning the composite performs more than twice as well as a simple sum of its components would predict. “It’s the magic of synergy,” Naraghi says. “A symbiotic composite between the foam and the struts.”

Adjust the thickness of those struts, or their spacing, or their angle, and the performance shifts. Thicker struts absorb more energy but also stiffen the foam; angling them in opposing cross-patterns changes the load path. A spacing of ten millimetres and a strut diameter of just under two millimetres uses only about five per cent of the total volume as added elastomer yet roughly triples the energy absorption relative to the base foam. Push the parameters further (denser struts, smaller gaps, just over one fifth of the volume filled) and the improvement approaches that tenfold figure. The design space is large, and it can be navigated from a standard 3D-printer gantry with a syringe swapped in for the filament extruder.

The Army’s immediate interest is helmets and blast-resistant seating. “Head and brain injuries remain a significant concern for the U.S. Army, and any material innovation that allows us to provide greater protection, while also managing comfort and keeping weights low, is a valuable step forward,” says Wetzel. Current military helmet padding absorbs impacts reasonably well but must be replaced after a significant blow, much as a bicycle helmet does. The IFAM composite is resettable: its interface between foam and struts is strong enough that after an initial performance dip (around 25 per cent in the first compression cycle, probably from minor debonding at the interface), subsequent cycles hold nearly steady, losing only another four per cent combined across nine further loading events. That durability matters enormously in any scenario where replacing equipment isn’t straightforward.

Manufacturing, too, looks tractable. A single syringe needle can inject more than a thousand struts per hour. An array of twenty-five needles working in parallel would, by the team’s estimates, produce over a thousand finished helmet pads in the same time. “Furthermore, the IFAM process is easily transferrable to scaled, real-world manufacturing,” says Wetzel.

The civilian applications reach further than helmets. Naraghi’s team is interested in child and passenger car safety seats, sports helmets, and motorcycle gear (“really any gear designed to absorb high-energy impacts,” as Naraghi puts it). There’s also a more speculative acoustic angle: the same internal skeleton that controls mechanical energy might, in principle, be tuned to damp specific sound frequencies. “The acoustic applications are still in the early research stages,” Naraghi acknowledges, “but we would like to explore this property more, to turn the foam into an active sonic filter that outperforms current materials.” The aircraft-cabin hum that sets in somewhere over the Atlantic; the persistent low-frequency rumble through apartment walls: those could, in theory, become targets.

Perhaps the most domestically appealing possibility is the simplest: furniture. “With our hybrid foam, you could have different zones of your cushion tuned to your different preferences,” says Naraghi. “For instance, firm for the neck, soft for the back, and medium for the legs.” One-size-fits-all foam, in chairs and mattresses and sofas, is the default partly because there’s never been a cost-effective way to do anything else. A computer-controlled syringe, working through a block of otherwise standard foam, might change that calculation. The same manufacturing process that could eventually outfit soldiers with better helmets could also, in a rather different context, produce a chair that fits the person sitting in it.

Source: Bruhuadithya Balaji, Frank Gardea, Eric Wetzel, Mohammad Naraghi, “In-foam additive manufacturing: Elastomeric cellular composites with tunable mechanics,” Composite Structures, Volume 383, 120158 (2026). DOI: 10.1016/j.compstruct.2026.120158

Frequently Asked Questions

Why does standard foam absorb impacts so poorly compared to this new material? Ordinary foam’s internal structure is essentially random: a disordered tangle of air pockets and polymer walls that collapses unevenly under load. The new approach injects precisely placed plastic columns into that foam, so the two materials brace and reinforce each other under compression rather than working independently. That cooperative effect, which the researchers quantify as a “synergy index,” is what drives the performance improvement; you’re not just adding material, you’re changing how the existing material behaves.

Could this actually make it into a helmet you’d buy in a shop? The manufacturing maths suggest it’s feasible at scale: the team estimates a 25-needle array could produce more than a thousand helmet pads per hour. The more immediate target is military helmets, where the Army Research Laboratory is already guiding the research toward deployment. Consumer sports and motorcycle helmets are on the roadmap, though timelines depend on how the military transition goes and whether commercial manufacturers pick up the process.

Does the foam wear out after a few big impacts? Less than you might expect. Single-use foams like expanded polystyrene are designed to crush once and be replaced; this composite takes a roughly 25 per cent performance hit after its first major compression, likely from slight debonding at the interface between struts and foam, but then holds nearly steady across subsequent impacts. In testing, nine further loading cycles produced only about four per cent more combined degradation, which is a very different durability profile from current resettable helmet padding.

What’s actually stopping engineers from tuning foam like this today? The core difficulty has always been that the two best approaches to foam engineering (mass-produced stochastic foams and precisely designed lattice structures) sit at opposite ends of a tradeoff between scalability and performance control. Cheap foams can’t be tuned; tunable lattices can’t be made quickly. IFAM sidesteps this by using the foam itself as both the structural host and the mould for the inserted struts, which means the precision layer can be added to an already-manufactured foam without rebuilding the production process from scratch.