Filament building up on the nozzle: causes and safe cleanup

This guide is for prints where a film, crust or small lump of plastic keeps collecting on the outside of the nozzle tip while it prints. It covers the causes printer makers document, which settings they say to change, and how Bambu Lab, Prusa, Creality and E3D say to clean the nozzle safely. Make sure you're in the right place:

What does the buildup do?

Bambu Lab describes it this way: "after a print has been running for a while, a small amount of molten filament builds up on the outside of the nozzle." It says this "can leave defects on the printed part, such as small gaps where material is missing and a rough surface," and that "in severe cases, the buildup grows into a blob around the nozzle and the print fails."

Bambu says noticeable buildup happens mostly with PETG-type filaments, "including standard PETG and PETG-CF." It says its own PETG Basic and PETG-CF "use specially optimized formulations, so they are far less prone to this than some other PETG and PETG-CF filaments on the market." Our PETG printing problems guide covers other PETG-specific fixes.

Cause 1: Damp filament

Bambu calls damp filament "one of the most common causes of buildup on the nozzle." Its explanation: "the moisture in the filament turns to vapor and expands as it heats up in the nozzle, which pushes the melt outward in all directions. Once some of that melt touches the outer wall of the nozzle, it sticks."

Bambu says to "dry PETG-type filaments before printing," and afterwards to store them in an AMS or a sealed box with desiccant, keeping the humidity below 20% RH. Our wet filament guide covers how to tell if a spool is damp and how to dry it.

Cause 2: Flow ratio set too high

Bambu says "extruding too much filaments also makes buildup more likely." For PETG-type filaments, it gives a flow ratio range of 0.93 to 0.96:

Bambu says its PETG Basic and PETG-CF both default to a flow ratio of 0.95, and to "try not to raise it." If the filament is dry and buildup continues, Bambu's order is:

1. Check the nozzle for wear.
2. If it's worn, replace it.
3. If not, lower the flow ratio slightly, to between 0.93 and 0.94.

Our worn nozzle guide covers how to spot wear. If yours needs replacing, our replacement nozzle shortlist matches parts to each printer.

If every wall also looks too wide, our over-extrusion guide covers flow calibration.

Cause 3: Temperature too high for the print speed

Bambu says "print speed and nozzle temperature have to suit each other." At very low print speeds, "the filament spends longer inside the nozzle, so it melts more thoroughly and the melt flows more freely," and unless the temperature comes down too, "you may see stringing, oozing, and buildup on the nozzle." So when you lower the print speed or the max volumetric speed, Bambu says to lower the nozzle temperature as well.

Starting from the default parameters, Bambu recommends:

1. Lower the nozzle temperature by 5 to 10 °C. "A less fluid melt is less likely to spread sideways at the nozzle tip and cling to the outer wall."
2. Lower the max volumetric speed by 4 to 5 mm³/s. "Extruding less material at a time reduces the chance of melt escaping and sticking."
3. Raise the max fan speed threshold by 10 to 20%. "More cooling sets the melt faster, so less residue collects on the outside of the nozzle."

Cause 4: A worn or loose nozzle wiper

On printers with a nozzle wiper, Bambu says the wiper "can wear down, work loose, sit too low, or break," and then "it no longer cleans the nozzle properly and residue stays behind." Its checks:

• Look it over for visible damage.
• Move it back and forth by hand.
• Power off the printer, push the toolhead over to the wiper, and compare their heights.

If you find a problem, Bambu says to repair or replace the wiper.

Cause 5: Lots of travel moves

Bambu says some models "involve a lot of travel moves, and a poor plate layout can add many more long ones." During those moves, "a fair amount of melt can ooze from the nozzle, get wiped onto its outer edge, and build up there." Its fixes:

• Lay parts out sensibly on the plate and keep long travel moves to a minimum.
• Increase the retraction length and speed a little. Bambu suggests 1.2 to 1.6 mm and 40 to 60 mm/s.

Our stringing guide covers retraction and travel settings in more detail.

Cause 6: A first layer printed too close

Bambu's first-layer guide says that if the first layer is "squished to the point where it's creating raised edges or dragging the nozzle, it's too low." Prusa says that with the nozzle too close, "the filament won't be able to 'flow out' leading to a potential clog of the nozzle," and its First Layer Calibration article adds "extrusion problems and clogging and poor print quality" to the list.

Don't assume PETG needs a higher nozzle, though. In its Live adjust Z article, Prusa says "PETG and other high-temperature materials require to be squished in the surface slightly more as they tend to warp (lift up), compared to the PLA." Set the height by reading the first-layer lines, as our first-layer lines guide explains.

Silicone socks and coated nozzles

Neither stops buildup on its own, but both change how easy it is to deal with.

• Prusa Nextruder silicone sock (CORE One family, XL, MK4/S, MK3.9/S). Prusa says the sock's main job is "to keep the temperature in the heater block stable," with the added benefits of "keeping your hotend clean from filament dirt and protecting it in case the print detaches." Prusa's blob article says "the component does not prevent extruder blobs" but "makes it easier to remove it." After fitting one, Prusa says to set LCD Menu > Settings > Hardware > Nextruder Silicone sock to ON.
• Bambu Lab X1 series sock. Bambu says the sock "helps to ensure the stability of the temperature of the nozzle," and to replace it when it's cracked, loose or broken.
• E3D ObXidian. E3D says its E3DLC coating "embeds non-stick properties into the Nozzle itself. Meaning considerably less plastic build-up around the Nozzle." E3D says glow-in-the-dark filament printed at high movement speeds can remove the coating.
• E3D Nozzle X. E3D's V6 nozzle cleaning guide treats Nozzle X differently from its other nozzles: it lists only nylon cleaning filament as a recommended method, and lists warm and cold pulls among the methods it doesn't recommend. It doesn't list a brass brush for Nozzle X.

How do you clean the nozzle safely?

Bambu, Prusa and Creality all soften the plastic with heat before removing it. Bambu's short version: "heat the nozzle first, then carefully remove the buildup."

A light film or crust

• Creality Ender-3 V3 KE: Creality's daily maintenance guide says that before each print, check "if there is any residual material on the nozzle. If present, heat the nozzle and remove the residue using a tool."
• Prusa Nextruder printers: Before fitting a sock, Prusa says to set the nozzle to 250 °C under Control > Temperature > Nozzle Temperature, wait about five minutes for the residue to soften, then clean the heater block and hotend with a brass brush. Then choose Preheat > Cooldown and wait until the hotend is below 50 °C before going on.
• E3D V6 nozzles: E3D's V6 nozzle cleaning guide lists a brass brush as the recommended external cleaning method for its brass, plated copper, stainless steel, hardened steel and ObXidian nozzles. It lists a blow torch as a method it doesn't recommend for any of its nozzles, and steel wire brushes as not recommended for brass, plated copper, stainless steel and hardened steel.

A blob around the hotend

A blob is the severe version. Bambu and Prusa both tie it to a print coming loose in the first layers: Prusa says "the blob forms if the first layer detaches from the print surface and sticks to the moving hot nozzle while it keeps extruding." Each maker gives a model-specific procedure:

Bambu's X/P, A1 and H2D blob guides note that "the hotend will automatically stop heating after being maintained at a high temperature for a certain period of time," so reheat if you run out of time. On the X and P series and the H2D, Bambu says not to press Home while the blob is there, "to avoid collision and potential secondary damage." Bambu softens the silicone sock and front housing with a hair dryer on its high setting, and warns against heating too long or too close.

If the hotend can't heat at all, Bambu has a separate procedure, demonstrated on the A1, and says "there is almost no simple way to fix this issue." Follow your maker's guide or contact support rather than improvising. Prusa says damage caused by a blob "is not covered by the warranty."

Prevention, per the makers

• Clean the build plate before printing. Bambu says the A1 blob "usually occurs when the plate is not correctly cleaned before printing."
• Check the first layer sticks across the whole plate, which Prusa says to confirm at the start of each print. Our print came loose guide covers why parts pop off.
• Watch the start of the print. Prusa says to stop "as soon as the filament starts to stick to the nozzle," and Bambu says to "stop the print immediately" if a blob forms.

A sensible order

1. Confirm the plastic is on the outside of the nozzle tip, not seeping from above it.
2. Heat the nozzle and clean off the buildup using your printer maker's method.
3. Dry the filament, especially if it's PETG.
4. Check the flow ratio. For PETG on Bambu printers, keep it within 0.93 to 0.96.
5. If you print slowly, lower the nozzle temperature by 5 to 10 °C.
6. Check the nozzle wiper, if your printer has one.
7. Reduce long travel moves, and raise retraction a little, staying under 2 mm.
8. Check the first layer isn't dragging the nozzle.

Checklist

• Buildup is on the outside of the nozzle tip, not leaking from the hotend.
• Nozzle cleaned hot, with cables kept clear of tools and brushes.
• Filament dried and stored with desiccant.
• Flow ratio not raised above the filament profile's default.
• Nozzle temperature lowered if print speed or max volumetric speed was lowered.
• Nozzle wiper intact, firm and at the right height.
• Parts laid out to keep travel moves short.
• Retraction under 2 mm.
• First layer not so low that the nozzle drags through it.
• Nozzle checked for wear, and replaced if worn.

How this guide was checked

This is a research-based guide. We haven't run these tests for it. Every cause, setting, temperature and cleaning step comes from the Bambu Lab, Prusa Research, Creality and E3D pages listed in the sources, retrieved on 2026-10-13. Temperatures and menu paths are kept to the printer models each page names. Read more in our editorial standards.

Print problems: what to check before you buy ↗