3D Printed Elemento Helmet: How Lattice Energy Absorption Works

• 1
  Why a 3D printed Elemento helmet absorbs impact differently
• 2
  Print orientation, strut diameter and the boundary conditions
• 3
  Material choice and where printed polymers stop
• 4
  What the 3D printed Elemento helmet teaches about hybrid design
• 5
  How to verify a printed energy-absorbing part
• 6
  Printed lattice versus machined or molded structure

A conventional helmet liner is expanded polystyrene. It is molded into one density, one shape, one thickness. Impact energy goes in, the foam crushes, and the cell structure that was molded is the cell structure you get. There is no way to vary stiffness across the shell without gluing in a second foam piece.

The 3D printed Elemento helmet replaces that single-density block with a printed lattice. A lattice is a repeated cell geometry, and the whole point of printing it is that stiffness can be tuned cell by cell. Thicker struts near the crown, thinner struts at the temple, a denser band around the rim where the shell meets the head. None of that requires a new mold.

Impact energy is absorbed by progressive cell collapse. Under load, the struts bend, then buckle, then densify. Each stage has a different stiffness, and the plateau between buckling and densification is where the energy actually goes. A lattice with a long, flat plateau protects better than one that goes from stiff to solid in a few tenths of a millimeter.

That plateau is a design variable. FEA and drop tests on printed coupons tell you where it sits. The mechanism is not magic; it is the same crush behavior engineers already model in honeycomb and foam, just with more control over where the crush starts and how far it spreads.

Directional strength is the first boundary. A lattice printed with vertical struts is strong in compression along the print axis and weak in shear across it. Rotate the part on the build plate and the same geometry behaves differently. Any printed structure that takes a load in more than one direction needs cells designed for the directions that matter, not a single uniform pattern.

Strut diameter sets the minimum feature size, and that size is limited by the printer, not the CAD file. Below roughly 0.4–0.6 mm, most powder-bed polymer machines lose strut fidelity: the strut prints thin, partially fused, or not at all. Design the lattice around the process window you can actually hold, then confirm with a printed coupon.

Layer height and build angle also set surface roughness on the struts. A 0.1 mm layer gives a smoother strut and a more predictable buckling load than a 0.2 mm layer. Roughness matters here because it acts as a stress riser. Small notches on a strut wall start the crack earlier than the FEA model predicts.

Finally, resin or powder removal. Hollow lattices trap uncured resin or loose powder. If the cells are too small or the drain paths too few, the part carries extra mass and, worse, trapped material that can shift the balance. Design drain paths and vents as part of the lattice, not as an afterthought.

Sports helmets in this class typically use a photopolymer or a laser-sintered nylon with elastomeric behavior. The requirement is a material that yields rather than shatters: it must take repeated small impacts and one large one without fragmenting. Glass-filled grades add stiffness but cut elongation, and that trade is usually wrong for an energy-absorbing liner.

Temperature is the usual failure point. Many printed photopolymers soften well below the temperature a dark shell reaches in summer sun. A lattice that passes a room-temperature drop test can lose half its plateau stiffness at 50–60 °C. If the part sees heat, the material data sheet needs numbers at that temperature, not just at 23 °C.

Humidity and UV add a slower effect. Nylon absorbs moisture, which changes stiffness and dimension over months. UV degrades many polymers at the surface. Coatings help, but they add mass and a process step, and they can also seal a lattice that was designed to be open.

This is where the boundary sits: printed polymers are excellent for low-density, complex, energy-absorbing geometry, and poor for high-point loads, sharp threads, and metal-to-metal bearing surfaces. Those features belong in a machined or molded component that is bonded or fastened to the printed body.

Almost every production helmet is a hybrid. The printed lattice handles energy absorption. A molded or machined shell handles stiffness, puncture resistance, and the anchor points for straps and adjusters. The printed part is rarely asked to do the whole job.

That split is a useful template for other products: impact guards, drone frames, prosthetic sockets, robot end effectors, protective housings. Print the geometry that is expensive to mold and cheap to vary. Machine or mold the geometry that needs tight tolerances, threads, or a hard bearing surface.

At GreatLight we see this crossover constantly. A team prints a lattice prototype to validate the energy curve in a week, then asks for the mounting ring, the strap anchor, or the insert in aluminium or stainless so it survives real loads and real torque. The printed part proves the concept; the machined part carries the load.

Two practical checks before you commit. First, does the printed feature carry a point load or a torque? If yes, plan a metal insert from the start. Second, does the assembly need a tolerance tighter than about ±0.2 mm? Printed polymer usually will not hold it across a full production run, and the mating part should be machined to ±0.005 mm instead.

Test the coupon before the part. Print a lattice block with the same cell, strut diameter, material, and orientation as the production geometry, then run it in compression. The curve you get is the real plateau, not the modeled one. It costs a day and it saves a redesign.

Then test at temperature. Run the same coupon at the top of the service range and at the bottom. A plateau that shifts 30 percent between 23 °C and 55 °C tells you the part needs a different material or a metal load path. Do not extrapolate from room-temperature data.

Then test the assembly, not just the coupon. Bonding, fasteners, and the shell interface change how load enters the lattice. A coupon that crushes cleanly can still fail at the bond line if the joint is stiffer than the cell next to it.

For the metal side of the assembly, the routine is more familiar: raw material check, in-process monitoring, final inspection, and reports on request. GreatLight holds ±0.005 mm on machined features and Ra 0.8–1.6 μm as a standard machined finish, with finer finishes down to Ra 0.2–0.8 μm when a bearing surface or seal groove needs it.