Infill patterns and percentage
Quick answer
Infill is the internal lattice a slicer builds inside a part, and for most functional prints, 15 to 25 percent grid or gyroid infill is a reasonable default; pushing infill past roughly 50 percent adds weight and print time far faster than it adds usable strength for most designs.
The material densities used in the weight example below are published specifications. The specific infill percentage ranges and pattern tradeoffs are widely shared workshop convention built from how slicers and their default profiles behave, not a single formal engineering standard.
What is infill, and why is it not just solid plastic?
Infill is the internal lattice structure a slicer builds between a part's solid outer walls and top and bottom layers. Printing a part fully solid uses far more filament and time than most designs need, so slicers instead fill the interior with a repeating pattern at a chosen percentage, trading some rigidity for a large reduction in material and print time.
Infill percentage is not a percentage of the part's strength; it is a percentage of the interior volume that is filled with plastic rather than left as internal air gaps.
How much does infill percentage actually affect strength?
Less than most people expect, especially past the first 20 to 30 percent. A part's outer walls and top and bottom layers do most of the work resisting bending and impact, since they are continuous solid plastic. Raising infill percentage mainly helps with crushing or compressive loads pushing straight into the part, and with resisting localized denting, rather than with bending strength along the part's length.
A part that fails under load with 20 percent infill usually fails again at 60 percent infill, just slightly later, because the actual weak point is often wall thickness, layer adhesion or print orientation rather than the amount of internal lattice.
Which infill pattern should I use for functional parts?
Grid and gyroid are reasonable defaults for most functional parts. Grid prints quickly and gives even support in two directions; gyroid gives fairly even strength in all directions and tends to print with less vibration and noise because it avoids sharp direction changes. Triangle and cubic patterns resist forces from multiple directions better than a simple grid, which matters for parts that will be loaded unpredictably rather than along one known axis.
Honeycomb offers strong shear resistance for its weight but takes noticeably longer to print than grid or gyroid at the same percentage, since its walls are not continuous straight lines. For most beginner projects, the choice of pattern matters far less than picking a reasonable percentage and print orientation.
How does infill percentage affect how much a print weighs?
Weight scales roughly with infill percentage plus the fixed weight of the solid shell. As a worked example using material density: a 50 mm solid cube in PLA, density about 1.24 g/cm3, would weigh roughly 155 grams if printed fully solid with no shell counted separately, since the cube's volume is 125 cm3 and 125 times 1.24 is about 155. The same cube at 20 percent infill uses only a fraction of that interior volume in plastic, which is why infill percentage moves material cost and print weight far more directly than it moves real-world strength.
This is also why comparing spool cost across materials only tells half the story. A denser material like PETG, at about 1.27 g/cm3, yields a heavier part than PLA at the same infill setting and geometry.
Does infill percentage affect print time as much as it affects weight?
Yes, and often more, since the printer has to physically move the nozzle through every infill line at whatever speed the slicer allows. Doubling infill percentage roughly doubles the time spent printing the interior of the part, though the outer walls, top and bottom layers stay the same regardless of infill setting. On a large part, going from 20 to 60 percent infill can add a meaningful fraction of total print time for a strength gain that may not be needed.
When does 100 percent infill actually make sense?
Solid infill is worth the time and material for small parts under genuine compressive load, such as a load-bearing bushing or a small mechanical part where wall thickness has no room to compensate. It is rarely worth it for larger decorative or lightly loaded parts, where the same strength improvement could usually be reached more cheaply by adding wall count (perimeters) instead of solid infill, since walls contribute more to bending strength per gram of plastic used.
Does infill choice change between PLA, PETG and TPU?
The pattern logic stays the same, but flexible materials like TPU are often printed with a lower infill percentage on purpose, since the goal is usually a part that compresses and flexes rather than one that resists rigid deformation. A stiff, high-percentage infill on a TPU part defeats the reason for choosing a flexible filament in the first place. Rigid materials like PLA, PETG and ABS follow the same infill guidance regardless of which one is chosen.
| Pattern | Relative print speed | Best for |
|---|---|---|
| Grid | Fast | General-purpose parts, quick prototypes |
| Triangle | Moderate | Parts loaded from multiple directions |
| Cubic | Moderate | Multi-directional loads, good compressive support |
| Gyroid | Moderate | Even strength in all directions, quieter printing |
| Honeycomb | Slow | High shear strength for the weight, decorative use |
Equipment mentioned here
- ELEGOO
ELEGOO ABS 3D Printer Filament 1.75mm Black 1KG Strong Layer Adhesion
$16.99 Check pricePrices change often - Polymaker
Polymaker ABS Filament Black 1KG 1.75mm, Heat Resistant, Strength
$17.10 Check pricePrices change often
Common questions
What infill percentage should I use for a general-purpose part?
Somewhere between 15 and 25 percent is a reasonable default for most non-structural parts, such as brackets, cases and prototypes. This range balances reasonable strength against print time and material use. Increase it only for parts under genuine compressive load, and consider adding wall count instead if the real problem is bending strength.
Does higher infill percentage make a part waterproof?
Not reliably. Waterproofing depends far more on wall thickness, the number of top and bottom solid layers, and how well layers bonded during printing than on infill percentage. A part can have 80 percent infill and still leak through a thin wall or a poorly bonded seam, while a well-printed part with a thicker wall and lower infill can hold liquid fine.
Which infill pattern prints the fastest?
Grid is generally the fastest common pattern, since its straight, repeating lines let the printer move at consistent speed without frequent direction changes. Honeycomb is typically the slowest, since its structure requires more direction changes and shorter line segments per unit of interior volume filled.
Should I use 100 percent infill on my first print?
No. A first print is better used to check bed adhesion, dimensional accuracy and layer quality, none of which improve meaningfully at 100 percent infill. Save solid infill for a specific part that genuinely needs it once basic print quality is dialed in, since it adds significant print time and material cost with little diagnostic benefit for a first attempt.
Does gyroid infill actually make a difference over grid for most parts?
For most everyday parts, the practical difference is small. Gyroid tends to print more quietly and gives slightly more even strength in every direction, which matters more for parts under unpredictable loading. For a straightforward bracket or enclosure loaded mostly one way, grid infill performs comparably and often prints a bit faster.