When you order a PLA print from us, one of the settings in the quote is infill, from 0% to 100% in 5% steps, with 20% as the default. This guide explains what that number means, what changing it does to your part and your price, and which setting to choose.
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Try it on your own model: change the infill in the quote and watch the price update.
What infill is
An FDM printer does not normally print a part solid. It prints the outside of the part as solid walls, with solid layers on the top and bottom, and fills the inside with a lightweight internal pattern, a bit like the honeycomb inside a door. That internal pattern is the infill.
The infill percentage is how dense that inside pattern is:
- 0% means the part is just its walls, top and bottom, with nothing inside.
- 20% means the inside is a fairly open grid.
- 100% means the inside is printed solid.
Infill only applies to PLA. Resin parts are always printed solid, so there is no infill setting for them.
What changing infill does
Strength and stiffness
More infill makes a part stiffer and better at resisting crushing and bending, and gives screws and inserts more material to bite into. The gain is not proportional, though. The outer walls carry much of the load, so going from 20% to 40% makes a noticeable difference, while going from 80% to 100% adds weight and cost for a smaller gain. Print orientation matters too: a printed part is weakest between its layers. Our guide to designing for FDM covers walls and orientation.
Weight
More infill means more plastic, so a heavier part. That matters for cosplay armour, drone parts and anything that hangs or is worn.
Print time
More plastic takes longer to lay down. On a large part, high infill can add hours.
Price
Our PLA prices are based mostly on the weight of plastic actually printed, plus a small charge for the part’s volume. More infill uses more plastic, so it costs more. On small parts, though, the $1 minimum price per PLA part often absorbs the difference.
Real examples from our quote
We ran these through our live quote tool. Prices include GST and are per part, before shipping ($15 per order, free on orders of $80 or more).
| Part | Material | 20% infill | 100% infill |
|---|---|---|---|
| 20 mm cube | Black PLA | $1.00 (minimum) | $2.55 |
| 30 x 20 x 10 mm block | Black PLA | $1.00 (minimum) | $1.92 |
| 30 x 20 x 10 mm block | Wood PLA | not measured | $2.50 |
| 30 x 20 x 10 mm block | Black resin | no infill choice | $5.76 (solid) |
The 20 mm cube uses about 3.15 cm³ of plastic at 20% infill and takes about 20 minutes to print. At 100% it uses about 8.0 cm³, around two and a half times as much. Both small parts land on the $1 minimum at 20%, so for small parts you can often raise the infill a fair way for little or no extra cost. On larger parts, the difference between 20% and 100% is much bigger in dollars.
Which infill to choose
| Use | Suggested infill | Examples |
|---|---|---|
| Display and decorative models | 10% to 20% | Figures, busts, vases, architectural models, ornaments |
| Light wearables and large props | 10% to 20% | Cosplay armour and helmets, where weight matters |
| General parts | 20% to 30% | Visual prototypes, enclosures, organisers, covers |
| Functional parts that take a load | 40% or more | Brackets, clips, mounts, handles, replacement parts |
| Small parts under high stress | Up to 100% | Small gears, pins and parts that are screwed or clamped hard |
A few notes:
- 0% suits only some shapes. With nothing inside, flat top surfaces have nothing to print onto and can sag. It can work for vase-like shapes; otherwise start at 10%.
- Thin parts are mostly walls anyway. On a thin clip or bracket, the walls make up most of the part, so infill has less effect.
- If you are unsure, go up a step on small parts. It is often free because of the $1 minimum.
Why 20% is the default
20% is a balance. It gives a part enough internal support for solid top surfaces and good general stiffness, while keeping the weight, print time and price down. Most display models, prototypes and household parts print well at 20%. It is also the default in a lot of printing software for the same reason.
Related guides
- Layer height guide: how layer thickness affects detail and time.
- 3D printing materials guide: choosing between the materials we sell.
- What affects the cost of a 3D print.
- PLA 3D printing and our online 3D printing service.
Frequently asked questions
What does 20% infill mean?
The inside of the part is filled with an open internal pattern that takes up about a fifth of the space, inside solid outer walls and solid top and bottom layers.
Is 100% infill the strongest?
It is the densest, but not always the best choice. The walls carry much of the load, so beyond about 40% to 60% the extra strength is small compared with the extra weight, time and cost. For small, highly stressed parts, 100% can make sense.
Does infill change how my part looks?
Not on the outside. The infill is hidden inside the walls. On very low infill, top surfaces can show slight dips or sagging.
Why didn’t my price change when I raised the infill?
Small parts often sit at the $1 minimum price for a PLA part. Until the plastic used pushes the price above that, changing the infill will not change what you pay.
Can I choose infill for resin prints?
No. Resin parts are printed solid, so the price follows the size of the part.