Should you use a cooling fan for ABS?

By Asked 3D Content TeamPublished Last verified

Should you use a cooling fan for ABS?

Mostly no: keep the part cooling fan off or low for ABS. PrusaSlicer’s Generic ABS profile leaves it off on normal layers, and Bambu Studio’s Bambu ABS profile runs it at 10%. Both raise it only for bridges, overhangs and layers that print in under 30 seconds: up to 25% in PrusaSlicer and 80% in Bambu Studio.

The number

Slicer and profile Normal layers Fast layers (layer time under) Bridges and overhangs Fan off for the first
PrusaSlicer, Generic ABS Off 15% (30 s) 25% 4 layers
PrusaSlicer, Generic ABS @MK4S Off 10% (30 s) 20% 4 layers
PrusaSlicer, Generic ABS @COREONE Off 15 to 20% (30 s) 25% 4 layers
PrusaSlicer, Prusament ASA 20% 20%, no boost 30% 4 layers
PrusaSlicer, Prusament ASA @MK4S 12% 12%, no boost 20% 4 layers
PrusaSlicer, Prusament ASA @COREONE 20% 20 to 25% (20 s) 25% 4 layers
Bambu Studio, Bambu ABS (X1 Carbon and P1S, 0.4 mm nozzle) 10% 10 to 60% (30 s) 80% 3 layers
Bambu Studio, Bambu ABS @BBL A1 Off 10 to 20% (30 s) 80% 3 layers
Bambu Studio, Bambu ASA (X1 Carbon and P1S, 0.4 mm nozzle) 10% 10 to 35% (35 s) 80% 3 layers
Bambu Studio, Generic ABS 10% 10 to 80% (30 s) 80% 3 layers

Values are read from PrusaResearch.ini in PrusaSlicer 2.9.6 and the BBL filament profiles in Bambu Studio 02.08.02.61, following each preset’s inherits chain to the parent that sets the value (fdm_filament_abs.json, fdm_filament_asa.json and fdm_filament_common.json for most Bambu figures).

Why print ABS with the cooling fan off?

Because ABS shrinks as it cools, about 1 to 2% according to Prusa, and a fan makes that cooling fast and uneven. Each new layer goes down hot on layers that have already shrunk, and the side the air hits cools first. Bambu Lab’s ABS/ASA guide says interlayer cracking happens when “the internal stress from cooling during printing exceeds the interlayer adhesion strength,” and lists “Fan speed too high” and a low chamber temperature among the causes. PrusaSlicer’s tooltip on “Keep fan always on” is blunter: “Useful for PLA, harmful for ABS.”

An open-top ABS box on a heated bed, cracked between two layers on the wall facing the part cooling fan, with the corner on that side lifted off the bedThe side the fan blows on cools and shrinks first, so the stress opens a gap between layers there and pulls the corner up.4Heated bed3Corner lifted off the bed2Part cooling fan1Crack between layers
  1. Crack between layers
  2. Part cooling fan
  3. Corner lifted off the bed
  4. Heated bed
The side the fan blows on cools and shrinks first, so the stress opens a gap between layers there and pulls the corner up.

Polymaker’s PolyLite ABS data sheet lists the cooling fan as OFF. Bambu Lab’s sheet allows 0 to 80% but pairs it with a 45 to 60 °C chamber: that warm enclosure lets the whole part cool slowly and evenly. Chamber targets are in what chamber temperature ABS needs.

Does cooling cause warping in ABS?

Yes, it makes warping worse. The same shrinkage pulls at the base: Bambu Lab’s warping guide says the outer edges “cool faster than the centre, creating tension that pulls corners up.” Bambu warns that “even a nearby open window, air conditioning vent, or desk fan can cool one side of a print faster than the other, causing uneven warping.” It lists a fast auxiliary part cooling fan as a cause too, since it “cools outer walls too fast”, and its ABS and ASA profiles set that fan to 0%.

Both slicers keep the part fan off for the first 3 or 4 layers, which PrusaSlicer’s tooltip says is “so that it does not make adhesion worse.” If a corner still lifts, see why a print warps on only one corner and whether bed temperature affects warping.

When does ABS need the fan?

On bridges, overhangs and layers too short to cool on their own. PrusaSlicer’s “Bridges fan speed” (25% in Generic ABS) “is enforced during all bridges and overhangs.” Bambu Studio’s “Fan speed for overhang” (80%) covers bridges and any overhanging wall where more than 25% of the line width has nothing beneath it. The basics are in what the part cooling fan does, with PLA and PETG speeds for comparison.

Short layers are the other case: a layer that prints in under 30 s, the trigger in both slicers’ ABS profiles, gets more fan. In Bambu ABS the speed ramps from 10% toward 60% as layer time falls from 30 s to 12 s, then holds 60%. Below a second limit (20 s in Generic ABS, 12 s in Bambu ABS) the slicer also slows the print so the layer has longer to cool. Small parts and thin towers hit this; see why small prints melt and go blobby.

Should the part cooling fan be on for ASA?

Low, like ABS, though the shipped profiles give ASA a little more. The Prusament ASA presets tick “Keep fan always on”, so every layer after the first four gets 12 to 20% where Generic ABS gets none, and bridges get 20 to 30%. Bambu ASA caps its short-layer boost at 35% instead of Bambu ABS’s 60%, but starts it below 35 s instead of 30 s. The data sheets repeat their ABS advice: OFF for Polymaker ASA, 0 to 80% for Bambu Lab’s ASA.

Prusa says ASA “warps less” than ABS, but large parts still need an enclosure. For the bed, see the ASA bed temperature.

How do you set the fan for ABS?

  • PrusaSlicer: Filament Settings, Cooling. Untick “Keep fan always on” so normal layers get no fan, and leave “Enable auto cooling” ticked. Set Fan speed Min and Max (15% in Generic ABS), “Bridges fan speed” (25%) and “Disable fan for the first” (4 layers). Under Cooling thresholds, “Enable fan if layer print time is below” holds the 30 s trigger.
  • Bambu Studio: Filament settings, Cooling tab, Part cooling fan. “Initial layer fan” keeps the first 3 layers at 0%. “Min fan speed threshold” and “Max fan speed threshold” set the two ends of the short-layer ramp (10% at 30 s and 60% at 12 s in Bambu ABS). “Keep fan always on” decides whether normal layers get the minimum or nothing. “Fan speed for overhang” sets bridges (80%), and the Auxiliary part cooling fan group below stays at 0%.

How to check it on your own print

  1. Start from the ABS or ASA preset for your printer and nozzle, not a PLA profile with the temperatures raised.
  2. Slice and switch the preview to fan speed (“Fan speed (%)” in PrusaSlicer, “Fan Speed” in Bambu Studio). Normal layers should read off or at the low minimum. Only bridges, overhangs and short layers should run higher.
  3. Close the enclosure before the print starts: the door and the top lid on a Bambu Lab printer.
  4. If layers split, lower the fan first: untick “Keep fan always on” or cut the maximum. Then raise the bed and chamber temperature and block any draft. Bambu also lists under-extrusion as a cause, fixed with a hotter nozzle or a slower print.
  5. If a corner lifts, check which side faces the fan, a vent or an open door, then work through glue and the ABS bed temperature.
  6. If bridges sag or small tops slump, raise only the bridge or overhang speed, or the maximum for short layers. Leave the normal-layer speed low.

Sources

  1. resources/profiles/PrusaResearch.ini at version_2.9.6, PrusaSlicer on GitHub (accessed October 24, 2026)
  2. src/libslic3r/PrintConfig.cpp at version_2.9.6, PrusaSlicer on GitHub (accessed October 24, 2026)
  3. src/libslic3r/GCode/CoolingBuffer.cpp at version_2.9.6, PrusaSlicer on GitHub (accessed October 24, 2026)
  4. fdm_filament_common.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  5. fdm_filament_abs.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  6. fdm_filament_asa.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  7. Bambu ABS @BBL X1C.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  8. Bambu ABS @BBL P1S 0.4 nozzle.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  9. Bambu ABS @BBL A1.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  10. Bambu ASA @base.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  11. Bambu ASA @BBL X1C 0.4 nozzle.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  12. Generic ABS.json at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  13. src/libslic3r/PrintConfig.cpp at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  14. src/libslic3r/GCode/GCodeEditor.cpp at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  15. src/slic3r/GUI/Tab.cpp at v02.08.02.61, Bambu Studio on GitHub (accessed October 24, 2026)
  16. Bambu Filament Technical Data Sheet V3.0, ABS, Bambu Lab (accessed October 24, 2026)
  17. Bambu Filament Technical Data Sheet V3.0, ASA, Bambu Lab (accessed October 24, 2026)
  18. ABS / ASA / PC Usage Guide, Bambu Lab Wiki (accessed October 24, 2026)
  19. Model Warping, Falling Off, or Collapsing, Bambu Lab Wiki (accessed October 24, 2026)
  20. ABS, Prusa Knowledge Base (accessed October 24, 2026)
  21. ASA, Prusa Knowledge Base (accessed October 24, 2026)
  22. PolyLite ABS Technical Data Sheet, Polymaker Wiki (accessed October 24, 2026)
  23. Polymaker ASA Technical Data Sheet, Polymaker Wiki (accessed October 24, 2026)