Infill Explained: Density, Patterns, and Real Part Strength
What infill percentage actually does to strength, weight, and cost — plus when 20% is plenty, when to go solid, and why walls usually matter more.
The Most Misunderstood Setting in FDM
Infill — the internal lattice inside a printed part — is where newcomers reach first when they want a stronger part, and it's usually the wrong knob. Doubling infill from 20% to 40% adds roughly 25-35% more material and print time but often yields only 10-15% more stiffness, because bending loads live in a part's skin, not its core. Understanding this saves real money on every order.
What Infill Percentage Really Buys
| Infill | Behavior | Typical use |
|---|---|---|
| 10-15% | Light, springy core; skin does the work | Visual models, lightweight enclosures |
| 20-30% | The engineering default; excellent stiffness/weight | Brackets, housings, most functional parts |
| 40-60% | Diminishing returns begin; better compression | Press-fit bosses, clamped zones, thread areas |
| 100% | Solid; maximum strength and mass | Small high-load parts, parts machined after printing |
Walls Beat Infill (Usually)
For bending and torsion — how most parts actually fail — perimeter walls contribute far more than core density, because stiffness scales with material distance from the neutral axis. The cost-effective strength recipe: 4-5 perimeters (1.6-2.0mm walls) with 20-30% infill beats 2 perimeters with 60% infill at similar weight, nearly every time. When customers ask us to 'make it stronger,' thickening walls is usually our first move.
Patterns: When They Matter
Pattern choice matters less than density, but the differences are real:
- Gyroid: near-isotropic strength, excellent for parts loaded from multiple directions; our default for functional parts.
- Grid/rectilinear: fast, fine for flat plates loaded in-plane.
- Honeycomb: strong in compression normal to the hex axis; heavier print-time cost.
- Concentric: follows part contours; useful for flexible TPU parts where uniform flex matters.
When to Actually Go Solid
Full density earns its cost in a few places: small parts under high point loads (a 15-gram clevis at 100% costs pennies more), regions that will be drilled, tapped, or machined after printing, thermal mass for heat-soak duty, and parts certified against a solid-material calculation. For everything else, tuned walls plus moderate infill is the engineering answer — and it's how we quote by default.
Let the Geometry Decide
Our quoting engine prices your actual geometry, and our production profiles pair sensible walls with gyroid infill tuned per material. Need a specific infill for a load case? Note it in the order — or describe the load and let our engineers pick the cheapest configuration that survives it.
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