Infill is the internal structure your slicer generates inside a 3D print. You see the outer walls and the top and bottom surfaces. Everything in between is infill — a repeating geometric pattern that supports the top surface layers and adds structural strength to the part. Most makers set it once in a profile and never think about it again. That’s usually fine. But knowing what infill actually does and when to change it puts meaningful control in your hands over print time, material use, and final part performance.
What Infill Actually Does
When a slicer processes a solid-looking 3D model, it doesn’t print it completely solid unless you ask it to. Instead it prints the outer shell (walls) and the top and bottom flat surfaces, then fills the interior with a sparse lattice structure at whatever density you set.
Infill serves two functions. First, it supports the top surface layers. Without any material inside, the top surface layers would have to bridge across empty space from wall to wall, which causes sagging and surface imperfections on anything wider than a few millimeters. Even 10% infill gives those top layers enough contact points to lay down cleanly. Second, it contributes to the structural integrity of the part. How much it contributes depends on the pattern and density, and how those interact with your wall settings.
What infill does not do is replace walls as the primary structural element. This is the most important misunderstanding about infill in FDM printing, and it changes how you should think about dialing in strength.
Infill Patterns Compared
| Pattern | Strength Profile | Print Behavior | Best For |
|---|---|---|---|
| Gyroid | Uniform in all three axes | Smooth continuous curves, no sharp direction changes. Very printer-friendly at high speeds. | General purpose default. Functional parts, display models, virtually everything. |
| Grid / Lines | Strong X and Y, weaker Z | Fast. Sharp 90-degree direction changes. More vibration at high speeds. | Quick decorative prints where speed matters more than part strength. |
| Cubic / 3D Honeycomb | Strong in all three axes | Medium speed. More complex moves than gyroid but similar all-direction strength. | Structural parts under multi-directional loading. |
| Honeycomb | Strong X and Y | Medium. Classic pattern, slightly more material than gyroid for equivalent area coverage. | Parts with consistent lateral loads in known directions. |
| Concentric | Strong perimeter, flexible core | Medium. Follows part outline with nested rings. | Flexible TPU prints, vase-mode objects, anything where flexibility is desired. |
| Lightning | Minimal (top surface support only) | Very fast. Generates only the minimum structure needed to hold up the top surface layers. | Figurines, display-only models, visual prototypes where speed matters and strength doesn’t. |
| Solid (100%) | Maximum in all directions | Very slow on large parts. Same as printing all top layers throughout the full height. | Logo caps, coins, small parts where full density is genuinely required. |
The practical takeaway: Gyroid is the correct default for almost everything. It’s the only pattern that’s simultaneously strong in all three axes, prints smoothly at high speeds, and works across every filament type. Switch away from it only when you have a specific reason.
Infill Density Guide
| Density | Use Case |
|---|---|
| 5-10% | Display-only models, lightweight decoratives, speed-priority prints. No mechanical load. |
| 15-20% | General purpose default. Deck boxes, household accessories, most hobby prints. The sweet spot for balance. |
| 25-40% | Functional parts under moderate loads. Tool holders, brackets, clips, snap-fit components. |
| 50-80% | High-stress parts. Before going here, try increasing wall count first — it’s usually more effective. |
| 100% | Small detail pieces (logo caps, coins, mana chips). Parts where solid density is truly required. |
The Wall vs Infill Rule
This is the most important principle in FDM structural design and the one most makers get backwards.
Walls carry the load. Infill fills the space.
In almost every real-world failure test, FDM parts fail at the walls and layer interfaces, not through the infill core. The infill core is compressed but the outer shells fracture first. This means adding walls has a larger structural impact than adding infill density.
Practical comparison:
Part A: 2 walls, 40% infill
Part B: 4 walls, 15% infill
Part B is stronger under most real load conditions. Part A uses more filament and takes longer to print. For a functional bracket or clip, Part B’s configuration is the smarter choice.
The rule to remember: Before increasing infill density for strength, increase wall count. Go from 2 walls to 3 or 4. Then reconsider whether infill density still needs adjusting.
How Infill Affects Time and Filament: Real Numbers
A practical example using an 80mm x 70mm x 60mm deck box body printed in PLA on a Bambu Lab A1 at 0.20mm layer height:
| Infill | Filament Used | Approx. Print Time | Strength Increase vs 15% |
|---|---|---|---|
| 10% gyroid | ~68g | ~1h 40min | — (baseline) |
| 15% gyroid | ~73g | ~1h 50min | ~8% improvement |
| 25% gyroid | ~82g | ~2h 10min | ~18% improvement |
| 40% gyroid | ~97g | ~2h 40min | ~28% improvement |
Going from 10% to 40% uses 43% more filament and adds 60% more print time for a 28% strength gain. For a deck box sitting on a shelf, that strength gain is irrelevant. For a load-bearing mechanical bracket, it might matter — but adding a wall is still more efficient. Match your infill to your actual use case.
Infill and Top Surface Quality
Top surface layers bridge across the infill below. Very low infill density (under 10%) leaves wide gaps for those top layers to span, which causes roughness, small pinholes, and a dimpled appearance on the top surface.
Minimum infill for clean top surfaces: 15% for most prints. For large flat top surfaces on display models, 20% gives the top layers better support.
The ironing solution: If you need a very clean flat top surface — a logo cap, a tabletop piece, a surface someone will read detail from — enable ironing. Ironing adds a slow finishing pass over the top surface at very low extrusion, smoothing the surface significantly. It adds 5-15 minutes to the print but the improvement is noticeable. Available in Bambu Studio under Quality > Ironing.
OreKo logo caps specifically: Printed at 100% infill with 9 top layers. The logo detail is 0.08mm layer height raised geometry. At 100% infill the cap is completely solid with zero risk of infill pattern showing through the fine detail. The extra print time is worth it for a piece that’s meant to be the visual centerpiece of the deck box.
Infill Settings in Bambu Studio
In Bambu Studio, infill settings are in the Process panel, Quality tab.
Sparse infill density: Your percentage. Default is 15% in most PLA profiles.
Sparse infill pattern: The pattern. Default gyroid in current Bambu profiles.
Top/bottom shells: Number of solid layers at top and bottom. Separate from infill density but interacts with it. More shells means less reliance on infill for surface quality.
Infill combination: When enabled, allows infill to span multiple layers rather than printing at every layer. Speeds up prints with no real structural cost on low-detail models. Enabled by default in draft profiles.
Infill/wall overlap: How far the infill overlaps with the inner wall. A small overlap (default ~15%) bonds infill to walls. Too high and you get over-extrusion artifacts at the wall interface. Default is usually correct.
Bridge infill density: Separate setting for bridge surfaces. Higher density bridges sag less. Default is fine for most bridges under 50mm.
OreKo Infill Settings by Model Type
Here’s how infill is configured across the OreKo catalog and why:
Deck box body pieces — 10-15% gyroid. The box is a structural shell, not a load-bearing part. Walls carry the snap-fit forces. Infill just needs to support the top surface and add minimal weight.
Logo caps and coin tops — 100% solid. Small pieces with fine surface detail. Completely solid gives maximum detail resolution on the logo geometry and eliminates any risk of infill pattern showing through the thin top layers above the logo relief.
Dollhouse furniture body pieces — 15% gyroid. Display items with no load. Clean enough top surface at this density for painted finishes.
Miniature windows and shutters — 100% on small components (shutter slats, hinge pins), 15-20% on larger frames. Small parts at any density below 60-80% can have structural weakness at critical thin sections.
Mold box frame — 20-25% gyroid. Functional piece that sees mechanical load from poured silicone. The extra infill provides meaningful stiffness for this use case.
Cosplay prop body sections — 10-15% gyroid. Large pieces where weight matters for wearability. Walls provide structural rigidity. Infill is minimal.
Frequently Asked Questions: 3D Printing Infill
What infill percentage should I use for most prints?
15% gyroid is the right default. It supports top surface layers, adds adequate strength for most hobby and functional prints, and keeps print times and material use reasonable. Only go higher when you have a specific strength requirement.
What is the strongest infill pattern?
Gyroid and cubic (3D honeycomb) provide the best all-direction strength for the density used. Gyroid is the practical choice because it prints more smoothly at high speeds, reducing vibration and ringing artifacts on fast printers like Bambu Lab. For parts loaded primarily in one direction, honeycomb can outperform in that specific axis.
Does increasing infill really make prints stronger?
Yes, but less than most people expect, and less efficiently than increasing wall count. Doubling infill from 15% to 30% might increase ultimate strength by 10-15%. Adding a wall (going from 2 to 3 perimeters) often increases strength by a similar or greater margin with less added print time. For most strength requirements, increase walls first.
What is lightning infill?
Lightning infill generates the absolute minimum structure needed to support top surface layers. It’s shaped like tree branches growing from the walls inward. Very fast, minimal filament. It produces no meaningful structural strength and is only appropriate for display models, figurines, and visual-only prints where appearance matters but the part won’t be handled roughly.
Why do my top surfaces look rough or have small holes?
Infill density is probably too low. At under 10%, top layers span wide gaps between infill lines and produce visible imperfections. Increase to 15% or add more top layers (increase top shells to 6-9) for cleaner top surfaces. Ironing (a slicer finishing pass) is the most effective solution for flat top surfaces that need to look smooth.
Can I mix infill densities in a single print?
Yes. Bambu Studio and PrusaSlicer support modifier meshes that apply different infill settings to defined regions of a model. This lets you make one section of a part dense and structural while keeping the rest light. Most hobby prints don’t need this level of control, but it’s available for complex designs.
What is infill overlap and should I change it?
Infill overlap is how far the infill pattern extends into the wall lines. A small overlap (typically 10-15%) creates a mechanical bond between infill and walls. Changing the default isn’t usually necessary. If you see visible gaps between infill and walls in the sliced preview, increase it slightly. If you see over-extrusion at wall interfaces, decrease it.
When should I use 100% infill?
For small parts where fine surface detail needs maximum support (logo caps, coins, small decorative elements) and for functional small parts that take concentrated stress (hinge pins, press-fit connectors). For anything large, 100% infill is almost always unnecessary and adds significant print time with marginal real-world benefit.
