Why Cooling Is More Important Than You Think
Every layer you print is hot, soft, and waiting to deform. The job of the part cooling fan is to freeze each layer in place fast enough that the next one lands on a solid foundation — not on a still-warm, slightly sagging surface. Get this right and you get sharp overhangs, taut bridges, and crisp surface detail. Get it wrong in either direction and the results range from drooping geometry to cracking layers to warped parts.
What makes cooling genuinely tricky is that the optimal setting changes completely with the material. PLA wants as much fan as you can throw at it. ABS wants almost none. PETG sits awkwardly in the middle. And high-performance materials like PA and PC react badly to any cooling at all. There is no single "good" fan speed — only the correct speed for the material and geometry you're printing.
Cooling solidifies filament. Fast solidification = better geometry detail and overhangs. But fast solidification also = weaker inter-layer bonds. For most materials and most prints, you want to bias toward more cooling. For structural parts and high-temperature materials, you want less.
The Two Fans: Don't Confuse Them
Before tuning anything, it helps to understand that most FDM printers have two completely different fans doing completely different jobs. Confusing them is one of the most common beginner mistakes.
The hotend fan (heatsink fan)
This fan cools the heatsink on the upper part of the hotend — the cold zone that's supposed to stay cold. Without it, heat creeps upward from the heatblock into the heatsink, melting filament before it reaches the melt zone and causing clogs known as heat creep. This fan is not something you tune. It should run at 100% whenever the printer is printing and for a few minutes after the hotend heats up. On Bambu Lab printers, it's managed automatically and you can't change it.
The part cooling fan (blower)
This is the fan that blows air directly at the just-extruded filament as it leaves the nozzle. On most printers it's a blower fan mounted to the toolhead, sometimes with a duct that channels airflow around the nozzle. On Bambu Lab printers, this is a radial blower that blows from both sides of the nozzle — which is a big part of why Bambu printers handle overhangs so well. Every cooling setting in OrcaSlicer and Bambu Studio refers to this fan, not the heatsink fan.
On the Bambu Lab X1 Carbon and P2S, the auxiliary fan (the large fan on the side of the enclosure) also affects part cooling. For enclosed printing of ABS and ASA, set the auxiliary fan to 0 and keep the enclosure door closed. For PLA in the enclosure, you can leave the door open or use the auxiliary fan to vent hot air.
Fan Speed by Material
This is the table most people search for. The ranges below are tested starting points — your specific printer, environment temperature, and print geometry may push you slightly in either direction, but these numbers are correct for the vast majority of prints.
| Material | Fan Speed | First Layer | Why |
|---|---|---|---|
| PLA / PLA+ | 80–100% | 0–20% | PLA has the lowest glass transition temp (~60°C) and needs aggressive cooling to hold geometry |
| PETG | 40–70% | 0% | Moderate cooling reduces stringing; too much causes layer delamination and brittleness |
| ABS | 0–15% | 0% | Rapid cooling creates thermal stress, warping, and layer cracking — enclose and limit fan |
| ASA | 0–20% | 0% | Same thermal sensitivity as ABS; slightly more forgiving but still needs a low fan |
| TPU (flexible) | 40–60% | 0% | Moderate cooling helps bridges and overhangs; too much stiffens the part mid-print |
| PA / Nylon | 0–30% | 0% | PA bonds poorly with rapid cooling; low or zero fan maximises inter-layer strength |
| PC (Polycarbonate) | 0% | 0% | PC requires a fully heated enclosure; any cooling causes severe warping and delamination |
| PLA-CF / PETG-CF | Same as base | 0% | Follow the base polymer settings; CF fill doesn't change the thermal behaviour |
One pattern stands out: the harder a material is to print (higher temperature, more warping tendency), the less cooling it wants. This is not a coincidence. High-temperature materials need to stay warm between layers so the fresh extrusion bonds properly to the layer below. Cooling them aggressively creates a cold, partially crystallised surface that the next layer can't bond to — which is why ABS and PA prints delaminate at layer boundaries when the fan is on.
First layer cooling should be 0% for almost every material. The first layer needs maximum time to bond to the build plate — running the fan during the first layer is a major cause of adhesion failures and warping. OrcaSlicer and Bambu Studio handle this automatically when you use their preset profiles, but if you're customising settings manually, always check that your first layer fan speed is off.
Bridges and Overhangs: Cooling Does the Heavy Work
Bridges and overhangs are where cooling makes or breaks a print — literally. Understanding what happens physically explains why the settings matter so much.
How bridges work
A bridge is a horizontal span printed across open air with no support below. The printer deposits a line of molten filament across the gap; gravity immediately pulls it down. The race is between the cooling fan solidifying the filament and gravity deforming it before it sets. Win the race and you get a taut, clean bridge. Lose it and you get drooping filament and a sagging, rough underside.
For PLA, 100% fan speed almost always wins this race for bridges up to 60–80mm. For longer bridges, reducing print speed to 25–30mm/s while keeping maximum fan gives the filament more time in the air cooling before the next span is deposited. The support structures guide covers what to do when bridges are too long to print clean at any fan speed.
How overhangs work
Overhangs are more nuanced than bridges. Each overhang layer must be partially supported by the layer below it — the outer edge of the new layer hangs in air, and only the inner part touches the previous layer. Cooling solidifies the hanging edge before gravity can pull it down enough to cause curl. The steeper the overhang angle, the smaller the contact area with the previous layer, and the more the fan has to do.
The Bambu Lab A1 Mini and A1's dual-sided fan design is specifically optimised for overhangs — the symmetrical airflow from both sides of the nozzle cools the just-deposited filament more evenly and quickly than a single-sided blower. This is a hardware advantage that genuinely shows up in overhang test prints. For PLA, Bambu Lab printers regularly achieve clean 65–70° overhangs without supports using default settings.
The Layer Adhesion Trade-off
Maximum fan speed isn't always the answer, even for materials that tolerate it. The reason is inter-layer adhesion. When a fresh layer is deposited on top of a fully cooled previous layer, the thermal bonding between them is weaker than when the layer below is still warm. For most prints — decorative objects, housings, low-stress mechanical parts — this difference is irrelevant. For structural parts that see real stress, it matters.
The geometry of the print also interacts with this. A tall, thin print (like a tower or a thin post) can fail from poor layer adhesion even in PLA at 100% fan, because each layer is so small and prints so quickly that the fan has fully cooled the surface before the next layer arrives. The fix isn't to reduce fan speed across the board — it's to print multiple copies at once (spreading the fan's attention) or to use the "slow down for small layers" feature in OrcaSlicer, which throttles the print speed for small layer cross-sections to ensure adequate cooling time per layer without over-cooling.
The Slow down for cooling feature in OrcaSlicer (Cooling tab → Slow down layer time) sets a minimum time per layer. If a layer would print faster than this threshold, the printer slows down until the threshold is met. This is the right lever for small, detailed prints — don't reduce fan speed, increase minimum layer time instead.
For PETG specifically, the layer adhesion trade-off is more pronounced than for PLA. PETG printed at 70% fan can delaminate under impact loads in ways that the same part printed at 40–50% fan would not. If you're printing functional PETG parts — brackets, clips, enclosures — keep fan speed on the lower end of the PETG range and add more walls rather than increasing fan for a stronger result.
OrcaSlicer Fan Settings Reference
OrcaSlicer has more cooling controls than most slicers, which is both its strength and a source of confusion. Here's a full map of what each setting does and where to find it (Filament tab → Cooling).
Bambu Studio (the official Bambu Lab slicer) exposes fewer of these controls but respects the filament profiles' cooling values. If you want fine-grained control over bridging fan speed and overhang-specific cooling, OrcaSlicer is the better choice — the per-overhang-angle fan speed control alone is worth the switch for users who print a lot of organic shapes.
Common Cooling Problems and Fixes
Drooping overhangs despite maximum fan
If overhangs are sagging even at 100% fan speed, the problem is usually print speed, not fan speed. Slow the overhang print speed to 20–30mm/s. The fan has more time to cool each segment of filament before the toolhead moves on to the next one. Also check that your part cooling fan duct isn't clogged — a partially blocked duct can dramatically reduce effective airflow even when the fan reads 100%.
Warping or layer cracking (ABS/ASA)
This is almost always too much fan for the material. Drop to 0% and print in an enclosure. If warping persists even with zero fan, check whether your enclosure is actually sealed — gaps let cold air in, which creates the same rapid cooling as a fan. The ABS filament guide covers the full warping fix workflow.
Sagging bridges in PETG
PETG is frustrating for bridges because it's adhesive and stays fluid longer than PLA. Increase bridge fan speed to the maximum your PETG settings allow (60–70%), reduce bridge speed to 20–25mm/s, and try raising the bridge infill direction in OrcaSlicer so bridges span the shortest possible distance. If bridges are very long, adding a support or redesigning the bridge into a V-arch is often more practical than fighting PETG's nature.
Poor layer adhesion / delamination
Reduce fan speed by 20% and reprint. If the delamination is on a specific area (like a thin post or tower), use the minimum layer time setting to slow down those layers rather than reducing fan globally. Also check nozzle temperature — low nozzle temp combined with high fan speed is a fast route to delamination on any material.
Stringing that persists after retraction tuning
Under-cooled filament is more fluid during travel moves, which makes stringing worse even with perfect retraction. If you've tuned retraction and still see strings on PLA or PETG, increase fan speed before touching retraction further. More cooling = less fluid filament = less material to string. This is covered in more detail in the stringing guide.
The single most impactful thing you can do with cooling settings is use the right fan speed range for your material. PLA at 0% fan looks terrible. ABS at 100% fan warps and delaminates. These aren't edge cases — they're what happens every time if you use the wrong setting. Get this right and most other cooling problems disappear.
Beyond the material setting, the most useful lever is bridge fan speed — always push it to the maximum your material allows, regardless of what you set for regular layers. And if you're printing small or detailed features that fail from poor layer adhesion, slow down for cooling (minimum layer time) is the correct fix, not a lower fan speed.
For Bambu Lab users: the stock filament profiles already have good cooling defaults for Bambu Lab filament. If you're using third-party filament, start from the closest Bambu profile and adjust fan speed based on the material category above. OrcaSlicer's per-material cooling settings give you even more control and are worth exploring once you've got the basics dialled in.