Infill density is the percentage of the interior volume of a 3D-printed part that is filled with material, as opposed to air. A part at 100% infill is solid plastic; a part at 0% infill is a hollow shell. Practical FDM parts for UAV airframes use 10–60% infill depending on structural requirements, with the lattice pattern (rectilinear, gyroid, triangular, honeycomb) determining how that material is distributed.
Infill density is the single most consequential slicer parameter for printed UAV airframes. Doubling infill density roughly doubles print time and material consumption while increasing compressive strength by only 50–80% (the relationship is sublinear). This means that a wing spar printed at 50% gyroid infill is not twice as strong as one at 25% — it is perhaps 1.6× as strong at 1.9× the weight. The engineering problem is identifying the minimum infill density that provides adequate strength for the expected load case, because every gram of excess infill is a gram that could have been payload, fuel, or battery.
The optimal infill depends on the platform’s intended lifecycle. A reusable survey drone’s wing rib might need 40% infill to survive fatigue cycling over hundreds of flights. An expendable strike drone’s wing rib may need only 20% to survive a single catapult launch and a few hours of cruise. A racing quadcopter frame optimizes differently again — high infill at motor mounts (vibration and crash loads) with low infill elsewhere (weight savings for agility).
Related terms
- Spar — the primary structural element whose infill density most critically affects bending strength
- Rib — chordwise members whose infill supports airfoil shape under aerodynamic loads
- Fatigue — the failure mode that determines minimum infill for reusable platforms
- Safety Factor — the margin between design load and failure that infill density must provide
- Composite — the alternative structural approach that printed infill competes with
- Wing Loading — the overall load parameter that drives structural requirements