6 Fixes for 3D Print Under-Extrusion & Gaps: Causes & Pro Tips

If your 3D print looks like swiss cheese… Read this.

You’re excited. Your slicer preview looks solid. You hit print, only to watch your part emerge with strange gaps in the walls, weird holes between lines, or the dreaded under-extruded spaghetti.

Gaps in 3D prints are a common frustration, especially for beginners, but they’re not random. They’re signals from your machine that something’s off: the flow, temperature, speed, or settings. The good news? Most of these issues are fixable.

In this guide, we’ll walk you through the exact causes of gaps in 3D prints and under-extrusion, how to identify them, and how to get your prints back to looking clean, strong, and professional.

What Do We Mean by 3D Print Gaps and Under-Extrusion?

Let’s quickly define a few terms so you know what we’re fixing:

a. 3D printed under-extrusion: Your printer is not pushing out enough filament to form solid layers.

b. 3D printed gaps in walls: Visible spaces between perimeters (especially in thin walls).

c. 3D printed gaps between lines: Voids between adjacent lines in infill or top surfaces.

d. 3D printed gaps in the first layer: Poor adhesion or missing areas at the base of your print.

e. 3D printed gaps in layers: Layers that don’t bond well, sometimes resulting in splitting.

Why Are There Gaps in My 3D Print?

Here are the top culprits:

1. Your Nozzle Can’t Keep Up (Partial Clogs)

(source: reddit)

Even a partial blockage can prevent your extruder from feeding a steady stream, causing “3D print under-extrusion”. Dust, old filament residue, or low-quality filament can cause this.

Fix it:

a. Do a cold pull to clean the nozzle.

b. Try printing a simple extrusion test.

c. Use high-quality filament (this matters more than you think).

2. Incorrect Extrusion Multiplier or Flow Rate

Too little material = visible gaps in 3D prints (perimeters and infill).

Fix it:

a. Increase your extrusion multiplier/flow rate slightly (start with 5%).

b. Print a single-wall calibration cube to dial it in accurately.

3. Print Temperature Is Too Low

(source: Pexels)

Filament doesn’t flow well at the wrong temp, leading to you 3d printing gaps in layers.

Fix it:

a. Check the manufacturer’s recommended temp range.

b. Bump up the temp in 5℃ steps until extrusion improves.

c. Watch your filament’s surface, glossy? Too hot. Matte and stringy? Too cold.

4. Inconsistent Filament Diameter

(source: istock)

Cheap filament may have uneven thickness, which throws off your flow rate.

Fix it:

a. Use digital calipers to measure the diameter in multiple spots.

b. Input the actual average diameter into your slicer (don’t trust the label blindly).

c. Consider switching to a filament with tighter quality control.

5. Wall and Infill Settings Are Misaligned

(source：freepik)

Sometimes your walls and infill don’t “meet up” properly, leaving a small unfilled region.

Fix it:

a. Try "infill overlap" settings in your slicer (e.g., 10–20%).

b. Increase wall line count or adjust wall thickness to be a multiple of your nozzle size.

6. Too Fast, Too Furious

High speeds can lead to filament skipping or missed steps, especially with Bowden setups.

Fix it:

a. Slow down your print speed (especially outer walls and top layers).

b. Check your extruder tension. Is it gripping the filament firmly?

Still can’t fix the gaps and need to get your parts printed urgently? Upload your design file and receive an instant quote from JLC3DP. We’ll get your prints professionally printed, smooth, and perfect.

Quick Fix Table: Causes vs. Fixes

Real-Life Case Study

Ali, a product designer prototyping custom cases for Raspberry Pi builds, kept running into weak top layers and wall gaps, especially on functional parts.

After a few failed prints, he:

 Ran a cold pull to clear minor clogs.

 Adjusted his infill overlap to 15%.

 Switched to JLC3DP's better-quality filament.

 Recalibrated his flow rate using a single-wall cube.

The result? Crisp perimeters, clean top layers, and solid parts that didn’t crumble under stress.

If you're printing functional or precision parts, using higher-quality material and tweaking your slicer profile can make all the difference. Services like JLC3DP’s 3D printing service help when you want pro-level results without the tuning headaches.

If you’re facing a print that’s also refusing to stick properly? Check out our guide on how to remove a 3D print stuck to the bed, bed adhesion problems can mimic extrusion issues.

FAQs: Gaps and Under-Extrusion in 3D Printing

Q: Why does my first layer have gaps?
A: It’s usually poor bed leveling or too fast of a first layer speed. Also check that your nozzle is close enough to the bed.

Q: Are small gaps okay?
A: Occasionally, yes. But consistent or large gaps affect structural strength and aesthetics. Better to fix them.

Q: How do I test for 3D print under-extrusion?
A: Print a single-wall cube and measure the thickness. If it's significantly smaller than expected, you’re under-extruding.

Q: What if I’ve tried everything and still get gaps in 3D prints?
A: It might be time to inspect your extruder gear, replace your PTFE tube, or even upgrade your hotend.

Final Thought: Don’t Settle for Gaps

Gaps in 3D prints don’t mean you’re a bad printer, just that your machine is giving you feedback.With the right tweaks and a bit of observation, you can eliminate under-extrusion issues for good. And if your part really matters (like a test-fit, mold, or functional part), remember you can always fall back on professional help. JLC3DP’s 3D printing service can deliver precise, gap-free prints, no calibration required.