Bambu Studio PLA Cooling Settings: What Every Number Actually Does (And Why Yours Says 100%)

If you opened Filament Settings, clicked Cooling, and found a wall of percentages and second counts, you’re in the right place. That tab looks simple until you realize nobody agrees on what to do with it.

Half the forum says run PLA at 100% and never think about it. The other half posts test prints proving 100% is wrecking your parts. Both sides have evidence.

Bambu’s own wiki tells you what each box is named. It never tells you what to put in it.

So I went and read the source. Bambu Studio’s filament profiles are open source, so the factory numbers for every printer model are sitting there in public, waiting for someone to line them up. Let’s start with the number that brought you here.

A note on scope: every value below is for Bambu PLA Basic in Bambu Studio. Generic PLA shifts some numbers (its max-fan layer time is 8s, not 4s), and OrcaSlicer ships its own profiles. The rule for reading them is identical; trust the digits on your screen over mine.

The Short Answer: Should PLA Run at 100% Fan?

Usually yes, and you can stop worrying about it. PLA goes soft early, so freezing each layer quickly is genuinely useful. How early depends on who you ask: Bambu’s own PLA profile lists a vitrification temperature of 45°C, while the community usually quotes 50-60°C. Different measurement, same conclusion. This stuff softens well below what other filaments tolerate.

PLA also shrinks very little as it cools, which is why it almost never warps the way ABS does. On the r/BambuLab thread asking this exact question, the answer Google surfaces puts the shrinkage at 0.01-0.02% and concludes there are no warping issues worth worrying about. Blowing a lot of air at PLA is not the crime some forum posts make it out to be.

But “100%” on your screen might mean something very different from “100%” on your friend’s screen. That’s worth two minutes of your time.

Turn the fan down when:

• You’re printing functional parts where layer bonding matters more than a crisp overhang
• You’re printing large, slow layers where each layer already has a minute to cool on its own
• Your room is cold and drafty

Leave it alone when:

• You’re printing normal decorative stuff
• Your model has a lot of overhangs
• Nothing is going wrong

Silk PLA deserves its own line, because the obvious advice is wrong. It’s tempting to reason that glossy filament wants gentler cooling. It doesn’t. Patchy gloss on silk comes from the slicer varying speed and fan mid-print, not from the fan being high. What you want is a fan that never changes, plus an outer wall speed that never changes. Bambu’s own silk profile spells out the speed half: dry the filament, and set the outer wall to 40-60 mm/s.

And here’s where your printer matters again. Silk ships at a flat 100% on the P1S, P1P, X1, X1C, P2S, X2D and the whole H2 family, so leaving it alone is genuinely the right move. But on the A1, A1 mini and A2L, silk defaults to the same 60-80% ramp as regular PLA — a fan that swings around mid-print, which is the exact thing that ruins gloss. If you own one of those, “leave it alone” is bad advice. Set the minimum to 100% so it stops moving.

Silk is also brittle, so it belongs nowhere near the “functional parts” line above.

That “nothing is going wrong” case deserves emphasis too. If your prints look fine, the best cooling tweak is none. If you want a starting point for a specific filament, our print settings finder is a faster path than guessing.

Why Your Cooling Tab Says 100% and Your Friend’s Says 60%

Bambu ships genuinely different PLA cooling profiles to different printers, and the gap is big. This is the part almost nobody writes about, and it explains most of the confusion in this topic.

Here are the factory defaults for Bambu PLA Basic on every current model, resolved from Bambu Studio’s profile source. Values are for the stock 0.4 nozzle:

Five distinct groups. Same filament, same company, same year.

Swapping nozzles doesn’t touch a single fan percentage in that table, so everything below holds whatever nozzle you run. It can shift the layer times, though: an A2L on a 0.2 nozzle waits 25 seconds instead of 6.

Look at the first row again, closely.

That’s the whole answer to your question. Fan speed is supposed to slide between a floor and a ceiling based on how long a layer takes. When the floor and the ceiling are identical, there’s nothing to slide between. The curve is a flat line. Your layer time settings do nothing, because every possible answer is the same answer. PLA on a P1S runs the part cooling fan flat out, start to finish, with one exception we’ll get to.

If you’ve ever changed a layer time value and sworn nothing happened, you were right. Nothing did.

Note where the X1 sits. Its ceiling triggers at 8 seconds instead of 4, which looks like a real difference until you notice both ends are still 100%. The layer time is decoration.

Now look at the P1P, which people casually lump in with the P1S. It ramps from 50% to 100%, and its floor is the lowest of any Bambu machine. The P1P and P1S are the same printer with a different shell, and they get opposite cooling philosophies.

The A1 family ramps too, 60% to 80%, and never reaches full speed at all. If you’re weighing that machine, our Bambu Lab A1 mini review covers what else it does differently.

Where these numbers come from: `github.com/bambulab/BambuStudio`, under `resources/profiles/BBL/filament/`. Each printer file inherits from a shared PLA base called `fdm_filament_pla` and only overrides what’s different. The A1, A2L, P1P and H2 files override the fan values. The P1S file doesn’t, so it silently takes 100% from the base. Every row above was resolved through its full inheritance chain in July 2026 rather than read off one screen.

A forum user named TXJustin reported the P1S versus A1 mini split in December 2024. His numbers match the source exactly, and nobody in the thread gave him a real answer.

The part nobody can explain

Here’s a genuine loose end. TXJustin also compared the PETG profiles, and those numbers check out against the source too:

For PETG, the P1S uses less fan than the A1 mini. For PLA, it uses more. As he put it, the P1S fan can’t be both better at cooling and worse at cooling.

The obvious guess is that an enclosed printer traps heat, so PLA needs more air. But that theory dies on the PETG numbers. And the P1P kills it a second time: it’s an open-frame P1S, and it uses less PLA cooling than the enclosed version, which is the opposite of what the theory predicts.

The likeliest read is that these profiles were tuned separately over time by different people, and the inconsistency is historical rather than intentional. That’s a guess, and it’s labeled as one. Nobody at Bambu has explained it publicly.

How Bambu Studio PLA Cooling Settings Actually Decide Fan Speed

One rule drives almost everything: fan speed is set by how long the current layer takes to print, interpolated between two thresholds. Learn this and the rest of the tab stops being intimidating.

Bambu’s wiki gives a clean example. Say your floor is 10% fan, paired with 30s, and your ceiling is 80% fan, paired with 3s. Then:

• Layer takes 30s or longer, fan drops to 10%
• Layer takes 3s or less, fan climbs to 80%
• Anything in between gets a straight-line interpolation

Think of it like a thermostat that watches the clock. The faster a layer prints, the less time that plastic has to firm up before the nozzle comes back around, so the more air it gets. Which is exactly why a P1S with both ends at 100% has no ramp at all.

The “100%” trap: five boxes, five meanings

This is where searching for an answer gets genuinely dangerous. The number 100 appears all over the Cooling tab, and it means something different every time:

That fourth row catches people constantly. It looks like a fan setting. It’s a geometry filter. Copying “100%” from a tutorial into the wrong box does something you did not intend.

Every Setting in the Cooling Tab, Explained

Only three of these are worth touching for PLA: the minimum fan threshold, Don’t Slow Down Outer Walls, and the overhang fan speed. The rest are either well-tuned already or actively dangerous to fiddle with. Here’s what each one does anyway, because knowing why you’re leaving something alone is different from not knowing it exists.

Definitions follow Bambu’s official documentation. The judgment calls are mine.

The layer-time group

These four work together as the rule from the last section, plus two switches that shape it.

One cost of that safety net that nobody mentions: it’s a common cause of patchy gloss. When small layers slow down for cooling, the plastic extrudes slower and sits hotter, and hotter plastic comes out shinier. One test of a vase-shaped model came out glossy at the top and bottom with a matte band around the middle, purely from speed changes. Switching the slowdown off fixes the banding, and evening out your overhang and outer wall speeds finishes the job.

Be careful with that one, though. On tall prints with genuinely short layer times, the slowdown is doing real work, and turning it off trades a cosmetic problem for a structural one.

Don’t Slow Down Outer Walls

Exempts outer walls from that slowdown. Turn this on for silk and glossy filament, not because it reduces cooling but because it stops the speed from fluctuating. Speed swings on a glossy surface show up as visible sheen bands. It also helps avoid faint Z-banding on any shiny print.

This is the setting to reach for before you touch a fan value. Combine it with an outer wall speed locked at 40-60 mm/s, and a fan that holds at 100% rather than sliding around.

The overhang group

Overhangs get their own rules, because they’re where cooling earns its keep.

One number here is quietly interesting. PLA triggers forced overhang cooling at a 50% threshold, while the generic base for all filaments uses 95%. PLA is tuned to grab overhangs far more eagerly than the house default.

The A2L goes further still at 25%, the only model that overrides it. Hold the pre-start fan point for the next section too.

Auxiliary Part Cooling Fan

The fan on the side of the chassis. It runs at a constant speed and ignores layer time completely. PLA defaults to 70%, or 75% on the H2 group. No auxiliary fan hardware means the setting is simply ignored.

Chamber / Exhaust Fan

Three fans, three jobs, and mixing them up is why “chamber fan settings” is a common search:

The exhaust fan manages chamber temperature and fumes. It is not cooling your part. There’s a separate speed for after the print finishes, also 70%.

PLA also asks for no chamber heating at all: `chamber_temperatures` sits at 0 in the base profile and PLA never overrides it. That field exists for the filaments that do want a hot box. ABS on an H2D asks for 65°C, and PA6-CF asks for 60°C. PLA wants the opposite of what those materials want, which is the whole reason its fan settings look so aggressive next to theirs.

If you hear a fan running on your P1S and can’t tell which one it is, this table is your answer.

Full Fan Speed at Layer

Off by default (`full_fan_speed_layer=0`). Enable it to force the fan to maximum starting at a layer number you pick.

The First Layer Exception

The part cooling fan is off for the first layer on every model, and you should leave it off. That’s `close_fan_the_first_x_layers=1`. Air on layer one means poor adhesion, and poor adhesion means a print that lets go halfway through.

The auxiliary fan is where it gets interesting. Most models switch it off for layer one too, but the P2S and X2D run it at 40% instead. Per Bambu’s docs, that puts gentle ambient airflow around the first layers while the part cooling fan stays off, no direct blast at the fresh extrusion. Deliberate design, and only those two machines get it.

One more detail worth noticing: the generic filament base disables the fan for 3 layers, while PLA only disables it for 1. PLA firms up fast enough that one layer is plenty.

A miniatures optimization test puts it bluntly: first layer fan must be zero or bed adhesion falls apart. If yours already is falling apart, cooling is usually not the culprit, and our guide on when your first layer isn’t sticking walks through the real causes.

Should You Turn the Fan Down? What the Testing Actually Shows

There’s real evidence the defaults are conservative. But the loudest piece of that evidence doesn’t measure what it claims to measure. Let’s take both sides seriously.

The case for turning it down

The most cited test is a post on r/3Dprinting with over 300 upvotes. The author spent a day running part cooling experiments on an A1 Mini with SUNLU PLA+ at about 24°C ambient. He built a custom 35° overhang test (35° being the steepest angle that doesn’t trip the default 50% overhang threshold) and manipulated layer times by printing dummy cylinders alongside the part.

His results:

Two of his observations hold up well. First, blower inertia: a fan takes time to spin up, and at high speed a sudden overhang arrives before it can respond. That’s a real constraint, and Bambu’s own Pre-start Fan Time setting exists precisely because of it. His theory and Bambu’s engineering agree.

Second, and more interesting: the slicer watches the clock but ignores volumetric flow. Compare rows two and three of that table. Identical duration, wildly different amounts of hot plastic, and the slicer commands the same fan speed for both. Bambu’s documentation confirms the interpolation is based on layer time alone. He’s found a genuine blind spot in the model.

He also claims Bambu’s default TPU profiles pin the fan at a constant 100%, which contradicts everything about printing TPU well. He’s mostly right, and the exception is more interesting than the rule.

Across all 135 instantiated TPU profiles, 95 do exactly what he says: TPU 85A, 90A, 95A, 95A HF and Generic TPU all sit at a flat 100%, the same degenerate curve as PLA. Every single one of the 40 exceptions belongs to one of the two TPU for AMS lines, which drop as low as 10%.

So his complaint holds for most of the catalog and not for the part Bambu revisited most recently. If gentle cooling is right for TPU for AMS, why is it wrong for TPU 95A? Nobody has said.

And the AMS line isn’t even internally consistent, which by now should feel familiar. Bambu’s TPU for AMS mostly runs 20-40%, but an A2L with the stock nozzle asks for 50-80%, and putting a 0.6 nozzle on that same A2L changes it to 30-60%. Same filament, same printer, different hole, different cooling.

A separate PLA warping guide lands in the same territory from a different direction, suggesting a drop from 100% to 80% to stop edges lifting.

The most careful version of this argument comes from an H2D owner on the Bambu forum, whose machine has a notably stronger cooling system. He calls the stock settings “more or less too strong (yet not strong enough in some cases),” and his complaints are specific rather than sweeping: 60% at a 100-second layer time looks too high for large prints, 100% over overhangs is too high for large surface internal bridging (he runs 80%), and the 75% aux fan is too much for large parts (he runs 10%, because his chamber only reaches 27°C in an Australian winter).

Note what he does with the first one: he flags it and then leaves it alone, because he hasn’t tested it enough to justify changing it. That’s the right instinct, and it’s rarer than it should be.

Where that test falls apart

Now the part you won’t see in the comments.

The post is titled “nuking part strength.” The author never tested part strength. All three experiments measured overhang curl by eye. Layer adhesion loss is inferred from theory, not measured. No tensile test, no break test, nothing. The headline claim and the evidence are about different things entirely.

It’s also n=1: one printer, one filament, one homemade test piece, one room temperature.

And one of his numbers is simply wrong. He reports the A1 Mini maxing at 100% fan for a 6-second layer. The official profile says the A1 Mini maxes at 80%, and TXJustin’s independent forum report agrees.

Two sources against one. He may have been reading an OrcaSlicer profile, or an older version, or misremembering.

So: take the observations seriously, discount the conclusion. The blower inertia point is sharp. The volumetric flow point is genuinely smart. “Your parts are weak” remains unproven.

The case for leaving it at 100%

The other camp isn’t wrong either. As covered up top, PLA’s material properties make it unusually tolerant of aggressive air. Bambu’s defaults aren’t tuned to be optimal, they’re tuned to be foolproof: crisp overhangs out of the box, on any model, for a user who will never open this tab. That’s a defensible trade, and most people won’t notice what it costs.

But cooling is a balance, not a dial that goes to “better.” Push it and overhangs improve while shrinkage lines and edge lifting get worse.

And here’s a caution against getting too excited about any of this. One P1S owner in that profiles thread had prints go bad after two good weeks, cleaned his nozzle twice on support’s advice with no clog to find, noticed his fan was pinned at 100%, and concluded he’d found his culprit.

He then tried the recommended cooling settings in both Bambu Studio and OrcaSlicer. Same bad prints. The fan wasn’t his problem. A suspicious default is not automatically your bug.

What I’d do: the three cases from the top of this article are worth an experiment. Everything else, leave the defaults. Print the same model twice, change one value, compare. And don’t copy anyone’s numbers, including mine. Your room, your filament, and your machine aren’t mine.

Why Your Cooling Changes Don’t Stick

You probably didn’t do it wrong. The AMS put it back.

When the AMS reads the RFID tag on a Bambu spool, Bambu Studio automatically loads the factory profile for that filament. Your edits get overwritten. You change a value, it looks saved, and next session it’s gone.

On a P1S this compounds into real confusion. You’re fighting two things at once: RFID reloading the profile, and the flat 100% curve that makes your layer-time edits do nothing even when they do stick. Two separate causes, one identical symptom.

Three ways out:

1. Save a custom filament preset. Safest and what I’d recommend. Your profile, your name, nothing overwrites it. 2. Edit the system profile file. Help > Show Configuration Folder > system > BBL > filament, find your filament and printer, follow the `inherits` line to the base file. Real cost: every Bambu Studio update wipes it and you redo the whole thing. 3. Change it manually each print. Tedious, zero risk.

This also solves a small mystery. If you open the P1S profile file looking for fan values, they aren’t there. Printer files only list what differs from the base, and the P1S doesn’t differ.

The numbers live in `fdm_filament_pla`. That inheritance chain is the same one you follow in option 2, which is why option 2 works at all.

Worth noting: third-party spools have no RFID tag, so nothing auto-loads and nothing gets overwritten. If you run third-party filament in the AMS, this problem mostly disappears, and you’ll need to dial in the profile yourself anyway.

How to Change PLA Cooling Settings (Step by Step)

1. In the filament section of your project, select your PLA, click the three dots, choose Edit 2. Open the Cooling tab 3. Change your values (start conservative, see below) 4. Save as a new preset with your own name. Do not overwrite the system profile 5. Next print, pick it from the Custom category

A conservative starting point for a P1S, if you want to experiment: drop the minimum fan from 100% to around 60-70% and leave everything else alone. That gives slow layers a break while keeping fast layers fully cooled, which is roughly what Bambu already ships on the A1. Change one thing, print the same model, compare.

How to confirm it actually worked: slice your model, then switch the preview to color by speed, and again by fan speed. You’ll see exactly where the printer slows down or spins up for cooling. A single solid color means nothing is fluctuating, which is exactly what you want on silk. That’s far more trustworthy than staring at numbers in a dialog and hoping.

Five Mistakes That Cost People Prints

1. Copying numbers from tutorials. There’s a filament vendor’s own tutorial telling viewers to set fan speed thresholds to 200%. Bambu Studio’s ceiling is 100%. That value gets clamped or rejected. If a guide tells you to enter an impossible number, close the tab.

2. Touching the first layer fan. It’s 0 for a reason. Turn it on and you’ve traded a working print for a slightly crisper first layer you’ll never see.

3. Switching on every advanced option at once. Take wall order. One miniatures test found Arachne plus outer-wall-first introduced layer lines on a model that printed fine on defaults; experienced forum users swear outer-wall-first fixes cooling-induced layer lines. Both are true: outer-wall-first gives a better outer wall and worse overhangs, so it depends on your model. A separate four-model test found the real winner is inner-outer-inner, which gets outer-inner’s surface without the Z-seam damage.

But it needs at least 3 walls, and Bambu’s default is 2. Below three, the slicer quietly falls back to plain outer-inner, the one that test called useless. Set your wall count to 3 first, then pick the order.

4. Adjusting fan without looking at speed. They’re the same problem. One test found that at 200 mm/s, enabling overhang slowdown clearly improved 55-70° overhangs for about 4 extra minutes on a 3.5-hour print. At 100 mm/s, turning it off gave more consistent results. Speed changes what cooling needs to do.

5. Forgetting the fan isn’t your only cooling. Room temperature, drafts, and whether your door is open all participate. That 25-second-layer test printing perfectly at 0% fan is really a story about ambient air doing the work for free.

FAQ

What are the best settings for Bambu Lab PLA? The defaults, for most people. Bambu tuned them to be hard to break, and they succeed at that. If you print functional parts, start by lowering the minimum fan threshold rather than the maximum, because slow layers are where the fan is doing the least good. Change one value at a time and compare against a control print.

Why does my Bambu Studio PLA cooling say 100%? Because you own a P1S, P1P, X1C, X1, P2S, or X2D. Those models inherit the shared PLA base profile, which sets both minimum and maximum fan to 100%. It’s the factory default, not something you changed. The A1 family gets 60/80% instead.

My cooling settings aren’t working. What’s wrong? Two likely causes. If the values reset between sessions, the AMS is reloading the factory profile from the spool’s RFID tag, and you need to save a custom preset. If the values stay but nothing changes in the print, you’re probably on a P1S-class machine where min and max are both 100%, so layer time has no effect on anything.

What are the P1S fan settings for PLA? On Bambu PLA Basic: fan floor 100% (triggered at 100s), fan ceiling 100% (triggered at 4s), auxiliary fan 70%, exhaust fan 70% while printing, first layer part fan off. Because the floor and ceiling are equal, the part cooling fan effectively runs at 100% for the entire print after layer one. If you’re running third-party filament under the Generic PLA preset, the ceiling triggers at 8s instead, though with both ends at 100% the practical result is the same.

What is Max fan speed threshold in Bambu Studio? It’s the fan speed used when a layer prints in the paired layer time or faster. It works with Min fan speed threshold as the two ends of a linear interpolation based on layer time. Fast layer, more fan. Slow layer, less fan.

What’s the difference between the chamber fan and the part cooling fan? The part cooling fan points at your print and freezes each layer. The chamber (exhaust) fan pulls air out of the enclosure to manage heat and fumes, and does nothing for your part’s surface quality. There’s also an auxiliary part cooling fan on the chassis side of enclosed models, which does cool the part but at a constant speed.

Should I turn the fan down to make stronger parts? Possibly, but nobody has actually proven the gain. The widely shared test claiming Bambu’s defaults destroy part strength judged its prints visually and never broke a single one. The theory is sound: more cooling means less layer bonding. The measurement doesn’t exist yet. If strength matters to you, test it on your own parts rather than trusting a headline.