Which Lattice Unit Cell Is Right for Your Part?

Engineers selecting lattice unit cell types often find that the available comparisons contradict each other: one source says the octet is strongest, another says the gyroid is better, and a third says it depends entirely on relative density. All three are right in their own context, which is what makes the decision genuinely difficult. A decision framework based on load case and process gives clearer answers than a single ranked list.

The two families of lattice unit cells

Lattice unit cells fall into two broad families, and the distinction matters structurally before you consider any individual cell type. Strut-based cells are frameworks of beams or rods connected at nodes; the structure carries load primarily along the member axes as tension and compression. Surface-based cells, which include the TPMS family (gyroids, Schwartz P, diamond surfaces, and others), are continuous curved walls that divide space into two interpenetrating regions; load is carried by the surfaces in bending and membrane action, spread across a continuous area rather than concentrated at nodes.

Each family has inherent strengths and weaknesses. Strut-based cells tend to be stiffer in compression at a given relative density, because their members align with load paths. Surface-based cells tend to be smoother in their stress distribution, more resistant to local buckling, and better at energy absorption, because a crack or buckle cannot propagate quickly along a continuous wall the way it can jump from node to node in a strut network. Choosing a family is the first decision; choosing a specific cell type is the second.

Strut-based cells: BCC, FCC, and octet truss

The body-centred cubic (BCC) cell places a node at the centre of a cube and connects it to the eight corners. It is simple to model and print, performs reasonably under compression, but is relatively compliant in shear because its members have significant bending components under certain load orientations. The face-centred cubic (FCC) cell connects the centre of each face to its neighbours, giving better isotropy than BCC, but still not fully stretch-dominated.

The octet truss is the strut-based cell most consistent with Fuller's geometry. It places struts along the edges of both a regular octahedron and a cube sharing the same space, producing a geometry that is fully triangulated in all orientations and therefore stretch-dominated: every member carries predominantly tension or compression rather than bending. Research comparing strut-based cells at equivalent relative densities has found the octet truss significantly stiffer and stronger in compression than BCC or FCC, in some comparisons by factors of several times. It also allows relatively open channels through the structure, which makes it a better choice than surface-based cells when fluid flow or powder removal needs to be maintained alongside structural performance.

Surface-based cells: gyroid and the TPMS family

A triply periodic minimal surface (TPMS) is a surface that repeats in three directions and has zero mean curvature at every point. The gyroid, the Schwartz P surface, and the diamond surface are the most commonly used TPMS cells in additive manufacturing. Their continuous, self-supporting walls can be printed without internal supports in most powder-bed and resin processes, which is a significant fabrication advantage. The absence of sharp corners and stress-concentrating nodes means cracks spread gradually rather than propagating suddenly at a weak joint.

The gyroid in particular shows good energy absorption: its continuous walls progressively buckle and fold under compressive loading without catastrophic collapse, dissipating impact energy across a broad plateau in the stress-strain curve. This makes it a strong candidate for helmet liners, midsoles, and other applications where controlled crush response matters more than maximum stiffness. The trade-off is that dense gyroid lattices trap powder in powder-bed printing. The interconnected channels of a gyroid are small and tortuous, making post-process depowdering slow and incomplete if the geometry is not designed with escape routes in mind. Thinner walls and larger cell sizes help, but the permeability disadvantage relative to strut-based cells is real and worth quantifying before committing to the gyroid for a powder-bed application.

Matching cell to load case

The load case is the clearest filter. Under uniaxial compression, the octet truss and other stretch-dominated strut cells outperform TPMS cells at the same relative density, because their members align directly with the applied force. Under multi-axial or shear loading, the advantage narrows because TPMS cells respond more isotropically: their curved surfaces carry force in multiple directions simultaneously, and their performance degrades less as the load direction rotates.

For impact and energy absorption, TPMS cells, particularly the gyroid, have a measurable advantage. Their progressive buckling means the stress-strain curve shows a long, flat plateau: the lattice carries a roughly constant force over a large deformation before it densifies. That plateau is what absorbs kinetic energy efficiently. A stretch-dominated strut cell tends to fail more abruptly once its members buckle, producing a less controlled crush response. For biological scaffolds, where surface area for cell attachment and fluid permeability for nutrient flow both matter, the diamond TPMS surface performs well because it has a high specific surface area and interconnected pores of relatively consistent size.

Matching cell to print process

Print process is the second filter, and it can override load-case preferences. Powder-bed fusion processes (SLS, MJF) leave unfused powder inside any enclosed or tortuous cavity. A gyroid at fine cell size and high relative density may be mechanically excellent but unprintable in practice because the powder cannot be removed. If the application demands powder-bed printing, either increase cell size to open the channels, choose a more open cell topology (octet or a coarser strut design), or design explicit drain holes into the part. Resin and DLS processes are more tolerant of complex internal geometry because the liquid can drain, but they have their own constraints on minimum wall thickness and cure-through depth for internal surfaces.

Extrusion-based processes (FFF/FDM) favour cells with manageable overhangs. The BCC cell, whose members run at 45 degrees, prints cleanly on most desktop machines without supports because the angles are within self-supporting limits. The octet truss has some horizontal members that require careful orientation or support structures, but can be printed cleanly when the part is oriented so the problem members are minimised. TPMS cells generally require orientation planning but can often be printed support-free because their curved surfaces provide gradual overhangs rather than sharp horizontal spans.

Relative density: the dial that changes everything

Relative density, the fraction of the bounding volume actually occupied by material, is often the most powerful variable in the design, outweighing cell type for many applications. Doubling the relative density roughly doubles the stiffness and significantly increases strength for most cell types, though the exact scaling depends on whether the cell is stretch-dominated (strength scales roughly with relative density to the power of one) or bending-dominated (strength scales roughly with relative density squared). An octet truss at low relative density often outperforms a gyroid at high relative density on stiffness, but the comparison reverses at equal densities if the load is impact rather than static compression.

Grading the relative density across a part, denser in high-stress zones and lighter in low-stress ones, is usually more efficient than choosing a single cell type and density for the whole part. This is the idea behind functionally graded lattices, and it connects directly to the compression-tension separation work that Sam Lanahan has developed at C6XTY: if you can identify which zones carry compression and which carry tension, you can design the lattice differently in each zone and get a much more efficient structure overall.

Key takeaways

• No single lattice unit cell is best for every application; the octet truss leads in compressive stiffness and flow, while gyroids and other TPMS cells lead in energy absorption and biological performance.
• Strut-based cells are stretch-dominated and stiffer in direct compression; surface-based TPMS cells are more isotropic and better at progressive energy absorption.
• Print process constraints, particularly powder removal in powder-bed fusion, can override load-case preferences and must be factored in before cell type is finalised.
• Relative density is often the most powerful variable; grading it across a part usually beats optimising a single cell type for the whole volume.

Related reading

• How to Design Lattice Structures for 3D Printing
• How Gyroid and TPMS Lattices Behave Under Load
• How Geometric Lattices Outperform Solid Material on Strength-to-Weight

Frequently asked questions

What is the strongest lattice structure for 3D printing?

In compressive stiffness, the octet truss is among the strongest strut-based cells at a given relative density because it is fully triangulated and stretch-dominated. For energy absorption under impact, gyroids and other TPMS cells perform better. "Strongest" always needs a load case attached to it, because the answer changes.

What is the difference between a BCC and an octet truss lattice?

A BCC (body-centred cubic) cell connects the centre of a cube to its eight corners with eight struts. An octet truss combines the edges of a regular octahedron and a cube to produce a fully triangulated, stretch-dominated frame that is significantly stiffer and stronger under compression at the same relative density. The octet requires more struts per cell but carries load more efficiently.

Why is the gyroid good for energy absorption?

Its continuous curved walls buckle progressively under compression rather than failing suddenly at a node. This produces a long, flat stress-strain plateau where the lattice absorbs a roughly constant force over a large deformation, converting kinetic energy into controlled structural deformation before the material densifies. Helmet liners and midsoles use this property deliberately.

How does print process affect which unit cell to choose?

Powder-bed processes (SLS, MJF) leave unfused powder trapped inside tortuous geometries; fine gyroid cells can become impossible to clean properly, weakening the part. More open strut-based cells or larger cell sizes help. Resin and DLS processes tolerate complex internal geometry better. Extrusion processes prefer cells with manageable overhang angles. The manufacturing route must be decided alongside the cell type, not after.

Does relative density matter more than cell type?

Often yes, especially for static mechanical properties. Doubling relative density typically doubles stiffness and substantially increases strength regardless of cell type. Grading density across the part, so high-stress zones are denser and low-stress zones are lighter, usually gives better results than choosing a single optimised cell type at a uniform density, because it applies material exactly where the loads are highest.