What Happens When You Run Out of Filament Mid-Print?
Brick by Brick Bulletin – Issue #8
Hey makers,
You’re hours into a print, everything is running smoothly, and then—bam! You run out of filament mid-print.
So, what happens next? Does the printer pause? Fail? Spit out an error? The answer depends on your printer setup, sensors, and how prepared you are.
Let’s break down what actually happens when you run out of filament and how to save your print if it does.
What Happens If You Run Out of Filament?
Here’s what different scenarios look like:
1️⃣ If Your Printer Has a Filament Sensor (Like the Bambu P1S)
✔️ The printer will pause automatically when it detects no filament.
✔️ It will wait for you to load new filament and resume the print.
✔️ No print failure—just a small pause in the process.
2️⃣ If Your Printer Does NOT Have a Filament Sensor
❌ The printer keeps running with no filament, extruding air instead of plastic.
❌ The print continues, but layers will be missing, ruining the entire model.
❌ You’ll need to manually pause the printer before it’s too late.
How to Fix a Mid-Print Filament Runout
🔹 If Your Printer Pauses Automatically
1️⃣ Load New Filament – Insert and extrude a bit before resuming.
2️⃣ Manually Purge Old Color (if switching filaments) – Run 10-20mm of extrusion to clear the nozzle.
3️⃣ Resume Print & Watch the First Few Layers – Make sure the print restarts smoothly.
✅ Your print continues without major issues!
🔹 If Your Printer Has No Filament Sensor (And You Catch It in Time)
1️⃣ Pause Manually ASAP – If you see filament running low, pause the print before it fully runs out.
2️⃣ Swap Filament – Load the new spool and manually extrude a little before resuming.
3️⃣ Resume Printing – The transition might not be flawless, but it’ll save the print.
⚠️ If you don’t catch it in time, the printer will have printed empty layers, making it nearly impossible to fix.
How to Prevent Running Out of Filament Mid-Print
🔹 Check Spool Weight Before Long Prints – If it feels light, weigh it! Most slicers give an estimate of filament usage (Bambu Studio, Cura, PrusaSlicer).
🔹 Use a Filament Sensor – If your printer doesn’t have one, there are external add-ons available.
🔹 Enable Runout Detection in Slicer Settings – Some slicers can pause automatically if they detect no extrusion flow.
🔹 Keep Extra Filament On Hand – Always have a backup roll nearby, especially for long prints.
Final Thoughts: Don’t Panic, Just Plan!
If you’re using a printer like the Bambu P1S, you’re safe—it’ll pause and wait for you. If not, keep an eye on long prints to avoid disaster.
Have you ever run out of filament mid-print? How did you save it (or did you have to start over)? Let me know!
Until next time, stay printing and stay prepared!
Stay creative,
Dillon H.
Brick by Brick 3D Printing