How to Fix Gaps Between Walls and Infill

Gaps between the outer walls and the infill usually mean the infill is not overlapping the walls enough, or the printer is under-extruding. The fix is to raise the infill/wall overlap a little (Orca’s documentation suggests staying around 10 to 15%), check that extrusion is calibrated, and make sure the infill is anchored to the walls. This guide covers each setting and what the slicer documentation says about it.

What gaps between walls and infill look like

You see a thin slit or void between the inside of the outer wall and the first infill lines, often visible on a failed print that has split open or on a cut-away. Infill lines look like they stop short of the wall instead of touching it. Walls can feel hollow or flex because the infill is not holding them.

These gaps are different from dips in the top surface, which are covered in fixing pillowing on top layers.

Why the gaps appear

3DXTech lists three causes: the infill/perimeter overlap is set too low, the printer is under-extruding, or the slicer is miscalibrated. The slicer docs explain why overlap matters. Cura describes infill overlap as “the amount of overlap between the infill and the walls as a percentage of the infill line width,” and says that “a slight overlap allows the walls to connect firmly to the infill.” Orca Slicer says the infill area “is enlarged slightly to overlap with wall for better bonding.”

Step 1: Raise the infill/wall overlap

This is the first setting to change. Cura calls it Infill Overlap Percentage, and the base definition file in Cura’s source code sets the default at 10. Orca Slicer calls it Infill wall overlap and measures it against the sparse infill line width, not as a fixed distance. 3DXTech recommends raising the overlap to 10 to 15%.

Raise it in small steps and reprint the same test part. Orca’s page recommends about 10 to 15% to avoid material buildup and rough surfaces, so more is not better.

Step 2: Check that the infill is anchored

PrusaSlicer says infill “is usually connected to the perimeters with a so-called anchor,” and that the anchor length setting controls how many millimeters connect the two. Setting it to 0 prints the infill independently of the perimeters. If the infill anchor is set to 0 in your profile, increasing it can help. Orca Slicer has the same pair of settings (anchor and maximum anchor length) and says a value of 0 uses the old connection method.

Step 3: Rule out under-extrusion

If raising the overlap does not help, the plastic may not be coming out in the right amount. 3DXTech says to check that the extrusion multiplier is calibrated. Under-extrusion also shows up as thin, gappy walls and weak layers, so follow how to fix under-extrusion to check for a wrong flow setting or filament problem. A partial clog is covered in fixing a clogged nozzle.

Step 4: Slow the infill down

3DXTech also lists slowing the infill speed to improve bonding. Try a moderate reduction and compare, keeping in mind the trade-off in print time that print speed versus quality describes.

Step 5: Keep gap fill on

Gap fill is a different feature: it fills narrow spaces between perimeters that are too thin for another wall. Orca’s documentation warns that gap fill “is contributing to the model’s strength,” so turning it off is not advised. It is not the setting that closes a wall-to-infill gap, but it is worth leaving alone while you tune overlap.

Check the maker’s guidance

Setting names, defaults and ranges differ between slicers and versions. Check your slicer’s own documentation and your printer maker’s profile guidance before changing values.