Few things are more frustrating than opening the printer's door to find fine cobweb stringing between features or rough, blobby walls. The good news is that most surface-quality problems on FDM prints share a small set of causes. Here is how to fix them on the four most common filaments.
The Four Surface Flaws and Their Causes
| Flaw | Primary Cause | Quick Fix |
|---|---|---|
| Stringing / cobwebs | High temperature, too little retraction, wet filament | Lower temp a few °C, raise retraction, dry the spool |
| Blobs / zits | Excess pressure at layer-start, poor wipe | Tune coasting & wipe, reduce flow slightly |
| Rough / uneven walls | Inconsistent flow, low wall count | Calibrate flow, use 3+ walls |
| Overheating / drooping | Insufficient cooling on overhangs | Increase fan, slow down, use support-free angles |
Tuning by Material
Different materials respond to the same flaw differently, so always tune with the filament in mind:
PLA
PLA+ Filament 1.75mm strings the most when kept too hot. Dropping the nozzle from 215°C to around 200-205°C and enabling retraction usually removes most cobwebs. PLA also loves strong part cooling, so keep fan speed high after the first layer.
PETG
PETG Filament 1.75mm is famously sticky and stringy. It needs slightly less cooling than PLA and a higher retraction distance. Slow the travel moves and lower the fan to 40-60% to let the slightly tacky surface set cleanly.
ABS
ABS Filament 1.75mm is prone to pulled corners and rough top surfaces from insufficient enclosure warmth. Keep the chamber sealed, minimise fan use and print a little slower to avoid layer delamination that reads as rough walls.
TPU
TPU Filament needs a slow print head, direct drive and no excessive retraction (which can clog flexible filament). Raise bed adhesion by slowing the first layer and using a release-friendly surface like a PEI plate.
A Simple Diagnostic Routine
- Dry the material first — moisture is the number one cause of stringing and surface pitting. A filament drying box removes the variable before you change any setting.
- Print a temperature tower to find the lowest clean temperature for the current roll.
- Calibrate flow so walls are neither over- nor under-extruded.
- Adjust retraction in small 0.5 mm steps until travel moves leave no threads.
When Hardware Matters
If stringing persists at clean temperatures, check the nozzle. A worn or partially clogged tip disrupts flow and causes both blobs and rough walls. Keeping a spare high-flow nozzle on hand lets you swap the variable out in minutes — see ANTINSKY High Flow Nozzle for Bambu Lab H2.
Put these steps in order and most FDM surface flaws disappear on the first pass. Consistent material, a dry spool and one calibration at a time are the whole secret.