Infill showing through walls: why the pattern prints on the outside

This guide is for anyone who can see the infill grid, diagonal lines or a "veiny" texture through the sides of a print, or who sees the reverse: thin gaps where the infill doesn't reach the walls. It covers what the slicer makers say causes each, and the settings Bambu Lab, Prusa, OrcaSlicer, UltiMaker Cura, Simplify3D and Polymaker document for fixing them.

What does infill showing through look like?

The makers describe the problem from different sides:

• OrcaSlicer: printing infill first means "the infill will slightly push out the printed walls where it is attached to them, resulting in a worse external surface finish. It can also cause the infill to shine through the external surfaces of the part."
• Cura: printing the infill first "leads to sturdier walls, but the infill pattern might sometimes show through the surface."
• Bambu Lab: with the infill/wall overlap set too high, "the model's surface will bulge, affecting appearance."
• Polymaker: lists "Visible Infill" as a problem, and recommends enough walls to "prevent infill patterns from showing through the surface."
• Simplify3D covers the opposite case: "small gaps between the edges of your infill" and the walls.

Showing through, or something else?

Step 1: Start from your maker's profile

Reset to the profile your printer maker provides for your printer, nozzle and filament, then print a simple test part. Note the wall count and infill settings it uses. Bambu Lab says "for most of the non-structural parts with low requirements for strength, you can directly choose the default 2 layers of walls and 15% fill density." Prusa says "Original Prusa profiles always use a minimum of two perimeters."

If you've changed overlap, wall order or line widths, put them back to the profile's values first, then change one at a time.

Step 2: Add walls

• Polymaker: "A minimum of 2–3 shells is recommended for standard prints to ensure structural stability and prevent infill patterns from showing through the surface." For visible infill, it suggests raising walls to 3 or more.
• OrcaSlicer: increasing Wall loops lists "reduce infill ghosting" among its effects, along with strength and rigidity, at the cost of print time.
• Prusa: "the strength of a model is mostly defined by the number of perimeters (not the infill)."

Where to find it:

Step 3: Adjust the infill/wall overlap

Each slicer has a setting that overlaps the infill with the walls "for better bonding," in the words of Bambu Lab and PrusaSlicer. Bambu Lab says too much makes the surface bulge, and Simplify3D raises the overlap to close gaps between infill and walls.

OrcaSlicer also has a separate setting with a similar name, Infill/Wall Overlap under Top and Bottom Shells, which applies to the top solid infill. Its wiki suggests 25–30% for that one, so don't mix the two up. Our gaps in top layers guide covers it.

If infill shows through, lower the overlap in small steps. Polymaker's fix for visible infill starts with "Reduce overlap." If you see gaps between infill and walls instead, raise it in small steps.

Step 4: Print walls before infill

The order the slicer prints walls and infill in each layer makes a difference.

• OrcaSlicer: Print infill first can cause infill to "shine through the external surfaces." If you use it, OrcaSlicer recommends "the Precise Wall, Inner/Outer/Inner wall printing order or reduce Infill/Wall Overlap to avoid the infill pushing out the external wall."
• Cura: Infill Before Walls says printing walls first "may lead to more accurate walls, but overhangs print worse," while infill first "leads to sturdier walls, but the infill pattern might sometimes show through the surface." In Cura's base definition (fdmprinter.def.json), Infill Before Walls defaults to on. Printer profiles may override this, so check yours.
• Bambu Studio: Print infill first is under Process, Quality, Advanced. Bambu says "infill" there means "all horizontal lines, including sparse infill, internal solid infill, top surface, bottom surface, and bridge." It's off by default in Bambu Studio's source.
• PrusaSlicer: Infill before perimeters, under Print Settings, Infill, Advanced (Expert mode), "will switch the print order of perimeters and infill, making the latter first." Off by default in 2.9.6.

Polymaker's infill page puts it differently. It says printing infill before walls "reduces 'veiny' surface textures but may compromise dimensional accuracy," and calls infill after walls the default that "prioritizes surface quality." Because the makers don't agree on this one, test both orders on your own part with everything else unchanged.

Wall order

The order of the walls themselves can matter too. OrcaSlicer recommends Inner/Outer/Inner "for the best external surface finish and dimensional accuracy as the external wall is printed undisturbed from an internal perimeter," and says it needs at least 3 walls. Bambu Lab says printing outer walls first "can minimize the imperfections and interlayer patterns on the surface caused by the squeezing or contraction of the lines inside the model," though seams "may be more obvious." Both makers say outer-first orders print overhangs worse.

Step 5: Check wall line width and wall thickness

Line width and wall count are linked:

• Cura: Wall Thickness "divided by the wall line width defines the number of walls." If you widen the wall line width without changing Wall Thickness, check the Wall Line Count it gives you.
• Polymaker: "Wall thickness must be a multiple of the nozzle diameter (or line width)," for example 0.8 mm for 2 lines or 1.2 mm for 3 with a 0.4 mm line.
• Bambu Lab: "For various diameter nozzles, it is usually recommended not to modify the default line width." If you do, Bambu suggests keeping it between 0.75 and 1.5 times the nozzle diameter. Line widths are under Process, Quality, Line Width.

If you've changed wall or infill line widths from the profile, set them back and see whether the problem changes. If you see slits between the wall lines themselves rather than at the infill, see our gaps between walls guide.

Step 6: Rule out under-extrusion and speed

Gaps between infill and walls can come from the extruder rather than the settings above.

• Simplify3D: if raising the outline overlap doesn't close gaps, "you should try decreasing the print speed." It explains that infill is "generally printed much faster than the outlines," and if it's too fast, "it will not have enough time to bond to the outline perimeters." Its example is cutting the default printing speed by 50%, then raising it gradually.
• Prusa: with under-extrusion, "you may notice gaps in and/or in between printed layers." Prusa suggests starting from "the stock filament profiles which are tailored for your machine, filament type, and nozzle size."
• Bambu Lab: for lines not touching the walls, "the most common problem" is a K-factor "incorrectly set to a very high value." It says a common mistake is entering 0.25 instead of 0.025 after Flow Dynamics Calibration, and that most regular filaments land between 0.02 and 0.04.

If lines look thin everywhere, work through our under-extrusion guide. If you raise flow, don't overshoot. Our over-extrusion guide covers flow calibration in each slicer.

What about translucent and light filaments?

Polymaker's fixes for visible infill include using "translucent-friendly patterns (e.g., Gyroid)" as well as reducing overlap and adding walls.

A sensible order

1. Look at what you see: infill pattern showing through, or gaps between infill and walls.
2. Reset to your printer maker's profile and print a test part.
3. For infill showing through, add walls, then lower the infill/wall overlap a little.
4. Check that walls print before infill, and try an outer-first or Inner/Outer/Inner wall order if your slicer has one.
5. Put wall and infill line widths back to the profile values.
6. For gaps, raise the overlap a little, slow down the infill, and check for under-extrusion.
7. On translucent filament, try gyroid infill.

Change one setting per print and keep the same test file, so you know what fixed it.

Print problems: what to check before you buy ↗