3D printing infill: strength, weight, and cost
By the 3D Printer on Demand team · Updated July 2026
Infill is the pattern printed inside a part. Most 3D prints are not solid plastic. They have a shell on the outside and a lattice inside. That inside lattice is the infill. You set it as a percentage. Zero percent is hollow. One hundred percent is solid. Infill controls how strong, heavy, and costly a part is. Most parts do well between 15 and 50 percent. And here is the secret most guides skip: adding one more wall often beats adding more infill.
What is infill, really?
Infill is the grid of plastic inside a printed part. Picture the inside of the part. It is rarely solid. Instead it holds a grid or honeycomb of plastic with gaps.
That inner grid is the infill. The walls you see on the outside are separate. They are called the shell or perimeters.
You pick an infill percentage. Higher percent means more plastic inside and fewer gaps. Lower percent means more empty space. The right number depends on the job the part does.
What infill percentage should you use?
Use 15 to 20 percent for most parts. Go higher only when the part carries load. You do not need to memorize much. A few common settings cover almost everything.
The table lays out the ranges that work. Above 50 percent, you get less extra strength for each bit of added plastic. That is why very few parts need to be solid.
| Infill | Good for | Notes |
|---|---|---|
| 0 percent | Hollow display shells | Needs a closed top to print clean |
| 15 to 20 percent | Models, covers, light-duty parts | The everyday default |
| 40 to 50 percent | Brackets and parts under real stress | A big jump in strength over light infill |
| 75 to 100 percent | Parts that must be very stiff | Heavy and slow, use only when needed |
How does infill change strength, weight, and cost?
More infill makes a part stronger and stiffer. It also makes the part heavier and more costly. Every extra percent adds plastic and print time.
The gain is not steady. Going from 15 to 40 percent adds a lot of strength. Going from 60 to 100 percent adds much less for a lot more plastic. So there is a sweet spot, and it is lower than most people guess.
Match the infill to the job. Use light infill for display parts and covers. Use more for parts that carry load or take a hit. Our 3D printing cost guide shows how this shapes your price.
Walls or infill: which adds more strength?
Walls, most of the time. Adding one more shell wall often makes a part stronger than raising the infill. Thicker walls carry load better than a dense center.
The reason is simple. Most of an FDM part's strength lives in its outer walls, not its core. A part with thick walls and light infill can be stronger than a part with thin walls and heavy infill. It also weighs less and costs less.
So when a part feels weak, add a wall before you add infill. Our design for 3D printing guide covers wall thickness in steps of 0.4 mm, plus ribs, which add even more strength for even less plastic.
What do infill patterns do?
The pattern is the shape of the grid inside the part. It changes how strong the part is and how fast it prints. You do not have to pick one. We set a sensible pattern for your part. But it helps to know what they do.
| Pattern | Strength | Speed | Best for |
|---|---|---|---|
| Lines or grid | Good | Fast | Everyday parts, the common default |
| Honeycomb | Strong for its weight | Slower | Parts that need strength without bulk |
| Gyroid | Strong in every direction | Medium | Parts that get loaded from many sides |
| Triangles | Strong side to side | Medium | Flat parts that flex in the plane |
What do we pick, and why?
We aim for a smart balance. We want the part strong enough for its job without wasting plastic. For most parts, that means 15 to 25 percent infill for display and light-use parts, and more for functional parts that carry load or take impact.
We also pick a pattern that fits the part. Grid for speed on simple parts, honeycomb or gyroid when a part needs strength from many directions. We set these defaults so you do not have to.
For PLA and PETG, you get an instant price with these defaults baked in. For PA-CF or TPU, we send a fast human quote.
How does infill affect your price?
More infill means more plastic and more print time, and both raise the price. Lighter infill lowers it. This is one of the easiest ways to bring a quote down without hurting a part that does not carry load.
You pay one flat price per part, and it drops as you order more, with steps at 10, 50, 250, and 1,000 parts. We hold your price for 30 days. See the steps on our pricing page, or upload your file to our instant quote to see your price now.
Quick takeaways
- Infill is the lattice printed inside a part, set as a percentage of how full the inside is.
- Most parts do well between 15 and 50 percent. Very few need to be solid.
- More infill means more strength, more weight, and more cost, but the strength gain slows down fast.
- Adding one more wall often adds more strength than raising the infill, and it costs less.
- You do not set infill yourself. We pick sensible defaults, and lighter infill lowers your price.
Have a part to print? Get an instant price.
Instant QuoteCommon questions
- What is a good infill percentage?
- For models and light-use parts, 15 to 20 percent is plenty. For parts that carry load, use 40 to 50 percent. Very few parts need to be solid. Above 50 percent, you add a lot of plastic for little extra strength, so that range is only worth it for parts that must be very stiff.
- Does more infill make a part stronger?
- Yes, but the gain slows down fast. Going from 15 to 40 percent adds a lot of strength. Going from 60 to 100 percent adds much less for a lot more plastic. There is a sweet spot, and for most parts it sits below 50 percent. Match the infill to the load the part actually sees.
- Does infill affect the price?
- Yes. More infill uses more plastic and more print time, and both raise the cost. Lighter infill lowers it. For a part that does not carry load, dropping the infill is one of the easiest ways to bring a quote down. Our quote page bakes sensible infill into the price for PLA and PETG.
- Is 100 percent infill ever needed?
- Rarely. A solid part is very heavy and costly, and it prints slowly. Most strong parts do just as well at 50 to 75 percent with thicker walls. Save full infill for the few parts that must be as stiff as possible and cannot spare any flex.
- For strength, should I raise infill or add a wall?
- Add a wall first. Most of an FDM part's strength lives in its outer walls, not its core. One more shell wall often beats a big jump in infill, and it uses less plastic. So when a part feels weak, thicken the walls before you raise the infill. Ribs help even more for even less plastic.
- What infill pattern is strongest?
- It depends on the load. Honeycomb is strong for its weight. Gyroid is strong in every direction, which suits parts loaded from many sides. Grid and lines are fast and fine for everyday parts. You do not have to choose. We set a pattern that fits your part and the job it does.
- Do I have to set infill myself?
- No. We pick sensible infill and a matching pattern for your part. Upload your STL to our instant quote for a price in seconds on PLA and PETG. For PA-CF or TPU, we send a fast human quote after a quick look at your file.