3D printing · Guide · By Mohammed Almuhanna · Updated
3D Print Infill: Percentage and Patterns
Infill is the internal lattice the slicer prints inside the solid walls of a part. Instead of pumping a model full of solid plastic, the slicer leaves the inside mostly hollow and braces it with a repeating pattern, so the part holds its shape without the weight, cost, and hours a solid block would take. More infill buys strength. Less infill buys a lighter part that finishes faster and uses less filament. Most people run far too much of it. I leave mine at 15 percent gyroid for almost everything, and when a part feels weak I add walls instead of cranking the fill. Below I cover what the percentage really means, which pattern to pick, how infill moves the four things that matter, and where your settings effort is better spent.
Infill percentage
Infill percentage is how much of the hollow interior gets filled with plastic. At 0 percent the inside is empty and the part is just walls and a top and bottom skin. At 100 percent the interior is solid. Everything useful happens in between, and the right number comes down to what the part has to survive.
For non-structural or display pieces, 0 to 10 percent is plenty: the part only needs to hold its own shape and look right. For everyday prints, 15 to 20 percent is the sensible default and is what most slicers ship with. For functional parts that take real load, brackets, jigs, mounts, run 30 to 50 percent. Reserve 50 to 100 percent for the rare part that needs maximum strength, or that you plan to drill, tap, or machine into, where you want solid material under the tool.
Past that there are sharp diminishing returns. Strength does not scale linearly with infill, so going from 20 to 40 percent helps a lot less than the numbers suggest, and beyond about 50 percent you are pouring in time and plastic for very little extra strength. For most parts the walls and the top and bottom layers carry more load than the infill does, so the shell is where strength really lives.
Infill patterns
The pattern is the shape of the lattice. Slicers ship a dozen of them and most you can ignore. A handful cover almost every job. The table below sorts the common ones by what they are good for.
| Pattern | Speed | Strength | Best for |
|---|---|---|---|
| Lines | Fastest | Weakest | Display parts where speed is all that matters |
| Grid | Fast | Decent all-round | General-purpose default, good balance |
| Triangles | Medium | Strong in-plane | Parts loaded sideways, good shear resistance |
| Cubic | Medium | Good 3D strength | Parts loaded from several directions |
| Gyroid | Reasonably fast | Strong in all directions | Isotropic strength, flexible parts, a popular default |
| Honeycomb / Hexagon | Slower | Strong | Strength where you can spare the print time |
To choose, start from your goal. Want pure speed on a part nobody will stress? Lines or grid. Want even strength no matter which way the load comes from, or a part that needs to flex without cracking? Gyroid, which is why it has become many makers' standard pick. Want the most rigid result and do not mind a longer print? Honeycomb. For parts pushed sideways, triangles hold up well; for loads from several angles at once, cubic.
What infill changes
Infill moves four things at once, and they pull against each other.
- Strength. More infill makes a part stiffer and harder to break, but with the diminishing returns above. The jump from 0 to 20 percent is huge; the jump from 50 to 100 percent is small.
- Weight. More infill is more plastic, so the part gets heavier in direct proportion to how much you add.
- Print time. The nozzle has to lay down every line of that lattice, so higher infill means a longer print, sometimes by a lot.
- Cost. More infill burns more filament, and the longer print time adds machine and energy time on top.
This is why 100 percent is almost never the right answer. You pay for it four times over, in weight, in time, in filament, in patience, and get strength you mostly cannot use.
Spend on walls before infill
If a part feels weak, the instinct is to crank the infill. Wrong move. Add walls first. The shell does most of the structural work, so raising the wall count from the default 2 to 3 or 4, and adding a couple of top and bottom layers, stiffens a part more per gram than the same plastic spent on infill would. Add walls and skins for strength and let the infill stay modest. For most prints gyroid at 15 percent is my default, maybe 20 on something that takes a bit more load, and it balances strength against time and filament without turning into a project.
Infill checklist
- Display parts: 0 to 15 percent, lines or grid, since they only need to hold their shape.
- Everyday prints: 15 to 20 percent, gyroid or grid, the all-round default.
- Functional parts that take load: 30 to 50 percent, gyroid or cubic.
- Maximum strength or parts you will drill, tap, or machine: 50 to 100 percent.
- Want a part stronger? Add walls and top/bottom layers before raising infill; the shell does most of the work.
- Remember the diminishing returns: past about 50 percent you pay a lot of time and plastic for little strength.
How infill moves the price
Infill moves both numbers that set a print's price, how much filament a part uses and how long it runs, and pushing the percentage up climbs both at once. Feed the filament weight and the print time from your slicer into the 3D print cost calculator and it rolls the extra material and the longer run into the cost, so a dense part does not end up looking cheaper than it really was.
Common questions
What infill percentage should I use?
For display or non-structural parts, 0 to 15 percent is plenty. For everyday prints, 15 to 20 percent is the sensible default most slicers ship with. For functional parts that take real load run 30 to 50 percent, and reserve 50 to 100 percent for parts that need maximum strength or that you will drill, tap, or machine.
Which infill pattern is best?
Gyroid is a strong all-round default: it gives even strength no matter which way the load comes from and handles parts that need to flex, which is why it has become many makers' standard pick. Grid is a fast general-purpose balance, lines are fastest for parts nobody will stress, and honeycomb is the most rigid if you can spare the print time.
Does more infill make a part much stronger?
Up to a point, then sharply diminishing returns. The jump from 0 to 20 percent is huge, but going from 50 to 100 percent adds little strength for a lot of extra time and plastic. For most parts the walls and the top and bottom layers carry more load than the infill does.
Should I add infill or walls to strengthen a part?
Add walls first. The shell does most of the structural work, so raising the wall count from the default 2 to 3 or 4, and adding a couple of top and bottom layers, stiffens a part more per gram than the same plastic spent on infill. Keep infill modest and let the shell carry the strength.