Retraction Settings: Length, Speed and Z-Hop Explained
Retraction pulls filament back and re-primes it around every travel move, and it's the setting people reach for first when strings appear — often before checking the two things (moisture, temperature) that usually matter more. Here's what each of the three retraction values actually does and Bambu's own numbers for each.
Three settings, three different jobs
Retraction length is how much filament the extruder pulls back before a travel move, relieving the pressure that would otherwise ooze out. Retraction speed is how fast that pull happens — too slow and the melt has time to keep oozing anyway; too fast on some filaments (TPU especially) buckles the material instead of pulling it. Z-hop lifts the nozzle slightly during travel so it can't drag across already-printed surfaces and smear strings into a mess.
Bambu's stock values (direct-drive, 0.4 mm nozzle)
| Material | Retraction length | Retraction speed |
|---|---|---|
| PLA / PETG (typical) | 0.4 mm | nil mm/s |
| PETG | 0.4 mm | — |
| TPU | 0.8 mm | 10 mm/s |
| Machine default (z-hop) | 0.4 mm | |
All Bambu machines are direct drive, which is why these numbers are so much shorter than the 4–7 mm figures common in old Bowden-printer advice online. Applying Bowden-scale retraction to a direct-drive machine over-retracts, and over-retraction is itself a clog risk: the machine's own retraction distance before a wipe is 0.8 mm, already short by Bowden standards.
The order that actually works
- Dry the filament and cool the nozzle first. Retraction is the third lever for stringing, not the first — see the stringing guide for why moisture and temperature usually matter more.
- Increase retraction length in small steps (0.1–0.2 mm) if strings remain after drying and a temperature drop, staying under about 2 mm on direct drive. Longer pulls on a direct-drive machine risk dragging molten plastic up into the heatbreak, where it cools and causes a clog — see the clogging guide.
- Leave retraction speed near the stock nil mm/s unless a specific material calls for less. TPU is the exception: keep it deliberately slow (around 10 mm/s) because fast retraction buckles soft filament in the feed path instead of pulling it back cleanly.
- Verify z-hop is on (Bambu default 0.4 mm) if strings drag across the top of a print rather than hanging cleanly between towers.
Klipper printers: firmware retraction is a separate path
Machines running Klipper (Voron, RatRig, and Klipper-based boards on Sovol's SV07/SV08) can use Klipper's own G10/G11 firmware retraction instead of the slicer's retraction settings. Klipper's own documentation is explicit that these are alternatives, not additive: retraction speed defaults to 20 mm/s and unretract speed to 10 mm/s in the firmware path, and most users pick one system or the other rather than running both. If retraction seems to be double-applying (excessive oozing pauses, or the opposite — clogging despite conservative slicer settings), check whether firmware retraction is enabled alongside slicer retraction.
Common mistakes
- Copying Bowden-era advice onto a direct-drive machine. If retraction length is above 3–4 mm on any of the machines in our knowledge base, it was written for a different extruder architecture.
- Chasing retraction before drying the filament. Wet PETG or nylon strings regardless of retraction settings — see the drying guide.
- Cranking retraction speed on TPU. This is the single most common cause of TPU-specific jams; keep it slow.
Frequently asked questions
What retraction length should a direct-drive printer use?
Bambu’s stock direct-drive values with a 0.4 mm nozzle are 0.4 mm retraction length for PLA and PETG, 0.8 mm at a slow 10 mm/s for TPU, and 0.4 mm z-hop. If strings remain after drying the filament and dropping the temperature, increase length in 0.1–0.2 mm steps and stay under about 2 mm — longer pulls drag molten plastic into the heatbreak and cause clogs.
Why is 4–6 mm retraction wrong on a modern direct-drive printer?
Because those figures come from old Bowden-printer advice, where a long tube between extruder and nozzle demanded 4–7 mm pulls. All Bambu machines are direct drive, so their stock retraction is just 0.4 mm — and over-retracting on direct drive is itself a clog risk, dragging molten plastic up into the heatbreak where it cools and sticks. If a profile shows more than 3–4 mm, it was written for a different extruder architecture.
Should I increase retraction first when I see stringing?
No — retraction is the third lever, not the first. Dry the filament and drop the nozzle temperature first, since moisture and temperature usually matter more; wet PETG or nylon strings regardless of retraction settings. Only if strings remain afterwards, raise retraction length in 0.1–0.2 mm steps. On TPU, never speed retraction up past about 10 mm/s — fast pulls buckle soft filament and cause jams.
Not sure which of these fixes applies to your print?
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- Stringing and oozing — Bambu Lab Wiki
- Config_Reference.md — Klipper3d/klipper (GitHub)