Bambu Lab Pressure Advance Calibration: Fix Bulging Corners and Blobs

You’ve dialed in your temperatures. Your first layer looks perfect. Your bed adhesion is rock solid. But every time you print something with sharp corners, you get these annoying bulges — little blobs of excess material at every direction change. Or maybe your corners are slightly rounded when they should be crisp. Or you’re getting weird artifacts on the seam line that make your prints look like they were made by a drunk robot.

The problem isn’t your printer hardware. It’s pressure advance — and if you haven’t calibrated it properly for your specific filament, you’re leaving print quality on the table.

I run six Bambu Lab printers at ADP Industries. An X1 Carbon, an X1E, a P1S, a P2S, and multiple A1 Minis running production 24/7. I’ve calibrated pressure advance on every single one, for every filament I use, and it’s one of the highest-impact calibrations you can do. The difference between default PA values and properly tuned ones is the difference between “good enough” prints and prints that look like injection-molded parts.

This guide covers everything: what pressure advance actually is at a physics level, how to run the calibration test on Bambu Lab printers, how to read the results, how to set your values in Bambu Studio, and the often-misunderstood interaction between PA and print speed. Let’s get into it.

What Is Pressure Advance and Why Does It Matter?

Pressure advance is a firmware feature that compensates for the elastic behavior of molten filament inside your hotend. That sentence probably didn’t help, so let me explain with an analogy.

Think of your extruder and hotend as a syringe filled with honey. When you push the plunger, the honey doesn’t come out immediately — there’s a delay because the honey is compressible and the syringe has internal volume. When you stop pushing, the honey doesn’t stop flowing immediately either — residual pressure keeps squeezing honey out even after you’ve stopped pushing.

That’s exactly what happens in your 3D printer’s hotend. The extruder gear pushes solid filament into the melt zone, but the molten plastic inside the nozzle acts like a spring. There’s a pressure buildup before extrusion really gets going, and there’s a pressure bleed-off after the extruder stops.

What Happens Without Pressure Advance

Without PA compensation (or with incorrect PA values), here’s what you see:

At the start of a line: Under-extrusion. The extruder starts pushing, but the internal pressure hasn’t built up yet, so you get a thin, weak start to every extrusion line. This shows up as gaps at the beginning of perimeters, especially visible on the first perimeter after a travel move.

At the end of a line: Over-extrusion. The extruder stops pushing, but the built-up pressure inside the nozzle keeps pushing plastic out. You get blobs and bumps at the end of lines, which is most visible at corners, seams, and anywhere the printhead changes direction.

At corners: This is where it gets really ugly. When the printhead approaches a corner, it decelerates. When the print speed drops, the extruder should also reduce its feed rate. But the built-up pressure in the nozzle keeps pushing material out at the previous rate. Result: bulging corners. The sharper the corner and the faster the print speed, the worse the bulge.

During direction changes: Any time the printhead changes direction — corners, curves, infill turnaround points — you get uneven extrusion because the nozzle pressure isn’t matching the actual movement speed.

What Pressure Advance Actually Does

Pressure advance solves this by looking ahead at the planned motion and pre-adjusting the extruder. Specifically:

Before a line starts: PA pushes extra filament slightly earlier, building pressure before the nozzle reaches the extrusion point. This fills the gap at the start of lines.
Before a line ends: PA retracts filament slightly earlier, bleeding off pressure before the nozzle reaches the end point. This prevents blobs at the end of lines.
Before corners: PA starts reducing extrusion before the deceleration point, preventing pressure buildup from creating corner bulge.
After corners: PA ramps up extrusion as the printhead accelerates out of the corner, preventing the thin start you’d otherwise get.

The PA value (sometimes called the K-factor or pressure advance factor) controls how aggressively this compensation is applied. A higher value means more compensation. Too low and you still get bulging. Too high and you get under-extrusion at corners because the firmware is overcompensating.

Every filament, temperature, and nozzle combination has its own ideal PA value. That’s why calibration matters — there’s no universal “correct” number.

How Bambu Lab Handles Pressure Advance

Bambu Lab printers use Klipper-based firmware (or a Klipper-inspired fork, depending on which printer you’re running), which includes a pressure advance implementation. The parameter is set per-filament in Bambu Studio, and Bambu’s default filament profiles already include PA values.

Here’s the thing though: Bambu’s defaults are conservative estimates designed to work “okay” across a wide range of conditions. They’re not optimized for your specific printer, your specific hotend condition, or your specific roll of filament. And “okay” is the enemy of “great” when you’re trying to produce sellable parts or precision components.

The good news is that Bambu Lab has built a pressure advance calibration test directly into Bambu Studio. You don’t need to download custom G-code files or flash anything. It’s a built-in feature, and it works well.

Before You Calibrate: Prerequisites

Don’t run pressure advance calibration on a cold start. PA calibration assumes your other settings are already correct. If your temperatures are wrong or your flow rate is off, your PA results will be garbage.

Here’s what should be dialed in first:

Temperature. Run a temperature tower or use a known-good temperature for your filament. If you’re printing PLA at 220°C when it should be at 205°C, your PA results will be skewed because viscosity changes with temperature.
Flow rate. Your flow multiplier should be calibrated. Over-extrusion and under-extrusion will mask PA effects and give you misleading results. If you haven’t done this yet, check out our flow rate calibration guide — do that first, then come back here.
First layer calibration. Your Z-offset needs to be correct. This doesn’t directly affect PA calibration (the test mostly looks at upper layers), but if your first layer is bad, the test print might fail. See our first layer calibration guide if needed.
Clean nozzle. Partial clogs change the pressure dynamics inside your hotend. If your nozzle is partially clogged, your PA value will be calibrated to the clog, not to normal operation. Do a cold pull or swap to a fresh nozzle before calibrating. Our nozzle and hotend guide covers maintenance procedures.
Dry filament. Wet filament pops and sputters, which creates inconsistent extrusion that makes PA calibration unreliable. If your filament crackles during extrusion, dry it first. This is especially critical for PETG, nylon, and TPU.

Running the Pressure Advance Tower Test

Bambu Studio includes a built-in calibration suite. Here’s how to access and run the PA calibration:

Step 1: Open Bambu Studio Calibration

Open Bambu Studio. In the top menu, go to Calibration. You’ll see a dropdown with several calibration options. Select Pressure Advance (it might also be labeled “PA Calibration” depending on your Bambu Studio version).

Step 2: Select Your Printer and Filament

Choose the printer you’re calibrating from the printer dropdown. Then select the filament profile you want to calibrate. This is important — PA is filament-specific. PLA, PETG, ABS, and ASA all have different ideal PA values because they have different melt viscosities.

Make sure the filament profile matches what’s actually loaded in your printer. If you’re using a generic PLA profile but you have a specific brand loaded, consider creating a custom filament profile for that brand. You’ll be storing the calibrated PA value in this profile, so it should match your filament.

Step 3: Choose Test Method

Bambu Studio offers two PA calibration methods:

Line Method (Recommended for most users): Prints a series of lines at different PA values. Each line is printed at a different PA factor, and you visually compare them to find the best one. This is faster and easier to read.

Tower Method: Prints a tower where each layer uses a slightly different PA value. You examine the tower and identify which height has the best corners. This takes longer but some people find it easier to evaluate.

I recommend starting with the line method. It’s faster to print and easier to evaluate, especially if you’re new to PA calibration.

Step 4: Set the PA Range

The calibration dialog will ask you for a start value, end value, and step size. For most filaments:

PLA: Start 0.01, End 0.06, Step 0.002
PETG: Start 0.02, End 0.08, Step 0.002
ABS/ASA: Start 0.02, End 0.07, Step 0.002
TPU: Start 0.04, End 0.15, Step 0.005
Nylon/PA: Start 0.02, End 0.10, Step 0.005

These ranges cover the typical ideal PA values for each material type. If you’ve never calibrated before, start with these ranges. If you already know your PA is somewhere around 0.04, you can narrow the range (say 0.02 to 0.06 with a smaller step) for finer resolution.

Step 5: Slice and Print

Click the slice button, then send it to your printer. The calibration print is small and fast — usually under 15 minutes for the line method, 20-30 minutes for the tower method. Don’t use a draft or speed profile for this — print at normal quality settings so the results are representative of your actual prints.

Important: Print with the same settings you normally use. Same temperature, same speed profile, same cooling settings. PA calibration at one set of settings doesn’t necessarily transfer perfectly to vastly different settings. If you print at 200mm/s normally, don’t calibrate PA at 50mm/s.

How to Read Pressure Advance Calibration Results

This is where most people get confused. The calibration print is only useful if you know what to look for.

Reading the Line Method

The line method prints multiple lines, each at a different PA value. Each line is labeled with its PA value (printed next to it in small text, or numbered so you can reference the settings).

What you’re looking for:

Perfect line: Consistent width from start to end. No blob at the start, no blob at the end, no thinning in the middle. The line looks like a perfectly uniform extrusion.

PA too low: The line will have a blob or widening at the end, and potentially at corners or direction changes. The start might look slightly thin. The excess material at the end is residual pressure pushing out extra plastic.

PA too high: The line will have visible thinning or gaps at the corners/direction changes. The firmware is overcompensating — pulling back too much filament, which starves the nozzle during deceleration.

How to pick: Find the line where the width is most consistent from start to end, with no visible blobs or gaps. If two adjacent lines look equally good, pick the lower one — slight under-compensation is less visible in real prints than slight over-compensation.

Reading the Tower Method

The tower method prints a calibration tower where each “band” or layer range uses a different PA value. The PA value typically increases from bottom to top.

Look at the corners of the tower at each height. What you’re evaluating:

Bottom of tower (low PA): Corners will likely have visible bulging — rounded bumps where the corners should be sharp. The lower the PA, the more prominent this bulge.

Middle of tower (moderate PA): Corners should get progressively sharper and cleaner as you move up. At some height, the corners will look crisp with no bulging and no gap.

Top of tower (high PA): If PA is too high, you’ll start seeing gaps or slight indentations at the corners. The perimeters might also look slightly thin in places because the firmware is pulling back too aggressively.

How to pick: Find the height where corners are sharpest without any gaps or under-extrusion. Note the PA value for that height. If there’s a range where everything looks good, pick the middle of that range.

Tips for Accurate Evaluation

Use good lighting. Angled light makes bulges and gaps much more visible. Photograph the test print with a light source at a low angle.
Use magnification. A phone camera zoomed in, a loupe, or even a magnifying glass helps you see subtle differences between adjacent values.
Compare the extremes first. Look at the lowest PA line/section and the highest. You should clearly see over-extrusion on one end and under-extrusion on the other. This confirms the test is working correctly. Then narrow down to the sweet spot in the middle.
If everything looks the same, your range is too narrow or your test isn’t printing at high enough speed to make PA effects visible. Widen the range and ensure you’re printing at your normal speeds.

Setting Pressure Advance in Bambu Studio

Once you’ve identified your ideal PA value from the calibration test, you need to set it in your filament profile so every future print uses it.

Method 1: Via Bambu Studio Filament Settings

Open Bambu Studio
Go to the Filament settings tab (the spool icon)
Select the filament profile you want to modify
Look for Pressure advance or PA in the filament settings — it’s typically under the “Advanced” section
Enter your calibrated value
Save the profile

If you’re using a built-in Bambu profile (like “Bambu PLA Basic”), you’ll need to create a copy first. Click the save icon and give it a custom name (like “Bambu PLA Basic - Calibrated”). This way you preserve the original and have your tuned version.

Method 2: Via G-code

If you want to set PA for a specific print without modifying the filament profile, you can add it to your start G-code or filament G-code in Bambu Studio.

The G-code command for Bambu Lab printers is:

M900 K0.04

Replace 0.04 with your calibrated value. You can put this in:

Filament Start G-code: Applied whenever this filament profile is used
Print Start G-code: Applied to a specific print job

For most users, setting it in the filament profile (Method 1) is cleaner and more maintainable.

Per-Filament PA Values

Here’s why I stress that PA is filament-specific. These are typical PA ranges I see across my six printers:

PLA (generic): 0.02 - 0.04
PLA (Bambu Basic/Matte): 0.025 - 0.045
PETG: 0.035 - 0.065
ABS: 0.03 - 0.055
ASA: 0.03 - 0.06
TPU 95A: 0.06 - 0.12
Nylon (PA6): 0.04 - 0.08

Notice those ranges. Even within the same material type, the ideal PA value can vary by 50-100% depending on the specific brand, color, temperature, and nozzle condition. That’s why “just use the default” doesn’t cut it for quality-critical work.

Pro tip: When you find a PA value that works great for a specific brand and color of filament, save it as a custom filament profile with a descriptive name. I have profiles like “eSUN PLA+ Black - Calibrated” and “Bambu PETG White - Calibrated” with all my tuned values baked in. It saves massive time when switching between filaments.

How Pressure Advance Interacts with Speed

This is the part that trips up intermediate users. You calibrate PA, everything looks great, and then you switch from a 0.20mm quality profile at 150mm/s to a 0.28mm draft profile at 300mm/s, and suddenly you’ve got corner artifacts again. What happened?

The relationship between PA and speed is real, but it’s more nuanced than “PA changes with speed.”

The Physics

Pressure advance compensates for the elasticity of molten filament. The amount of compensation needed depends on:

Print speed: Higher speeds mean more pressure builds up in the nozzle (more filament is being pushed through per second). The deceleration at corners is more aggressive at high speeds, so the pressure differential is larger.
Acceleration: Higher acceleration values mean faster speed changes, which means the pressure dynamics are more extreme. A printer accelerating at 20,000 mm/s² experiences much more dramatic pressure swings than one at 5,000 mm/s².
Volumetric flow rate: This combines speed and line width and layer height. A 0.4mm line at 200mm/s pushes way more plastic through the nozzle per second than a 0.4mm line at 50mm/s. Higher volumetric flow means more pressure buildup.

What This Means in Practice

For most filaments and most speed ranges on Bambu Lab printers, a properly calibrated PA value will work well across a reasonable speed range. If you calibrate at 150mm/s and print at 200mm/s, you probably won’t notice a difference.

But if you calibrate PA at 80mm/s and then print at 300mm/s, the optimal PA value may actually shift. At much higher speeds, you might need a slightly higher PA value to compensate for the increased pressure dynamics.

My recommendation: Calibrate PA at the speed you print most often. For most Bambu Lab users doing quality prints, that’s somewhere in the 100-200mm/s range. If you also do a lot of draft/speed printing at 250mm/s+, consider calibrating PA separately for your speed profile and saving it as a different filament preset.

PA and Input Shaping

Bambu Lab printers also use input shaping (resonance compensation) to reduce ringing artifacts at high speeds. PA and input shaping work on different problems but they interact in the acceleration/deceleration phases.

Input shaping smooths out the motion commands to reduce vibration, which also affects how quickly the printhead actually accelerates and decelerates. This means the effective acceleration profile that PA “sees” is already shaped by the input shaper.

For more details on how input shaping works, see our input shaping guide.

The practical implication: calibrate PA with input shaping enabled (which is the default on Bambu Lab printers). Don’t disable input shaping for PA calibration — you want PA tuned to the actual motion profile your printer uses.

Common Pressure Advance Problems and Fixes

Problem: Corner Bulging Even After Calibration

If you’ve calibrated PA and you still see corner bulge, consider these causes:

Speed too high for your PA value. If you’re printing at extreme speeds (300mm/s+), your PA value from a moderate-speed calibration might be insufficient. Re-calibrate at the actual print speed.
Flow rate too high. Over-extrusion makes corner bulge worse because there’s already excess material. Check your flow rate calibration.
Temperature too high. Overly hot filament is more fluid and more susceptible to pressure effects. Try reducing temperature by 5°C.

Problem: Gaps at Corners After Setting PA

You’ve overcompensated. Your PA value is too high, and the firmware is pulling back too much filament at corners.

Lower your PA value by 0.005-0.01 increments until the gap disappears.
Check your retraction settings. If retraction is happening at corners (it shouldn’t for perimeters, but check), it can compound with PA to cause gaps.

Problem: Seam Bulge

PA helps with seam quality but doesn’t fully control it. Seam artifacts are also affected by:

Seam position settings in Bambu Studio (aligned vs. random vs. nearest)
Retraction at layer change settings
Wipe distance settings
Coast distance (not available in all profiles)

If your seam is bulging, PA might be part of the solution, but also look at the seam-specific settings in your print profile.

Problem: Different PA Needed for Different Colors

This is real and it catches people off guard. Different colorants change the melt properties of filament. Black PLA and white PLA from the same manufacturer can have noticeably different ideal PA values because the pigments (carbon black vs. titanium dioxide) affect viscosity.

If you’re doing color-critical work, calibrate PA per color. For casual printing, calibrate for your most-used color and accept minor variations on others.

Problem: PA Value Seems to Change Over Time

If your PA calibration was perfect last month but now corners look bad:

Nozzle wear. A worn nozzle has a slightly different orifice geometry, changing pressure dynamics. Swap to a fresh nozzle and recalibrate.
Filament moisture. Wet filament has different flow properties. Dry your filament and re-test.
PTFE tube degradation. On printers with PTFE-lined hotends (A1/A1 Mini), the tube degrades over time and changes friction. See our maintenance schedule for PTFE replacement intervals.

Advanced: Multi-Material PA Considerations

If you’re using the AMS for multi-material prints, each filament slot can have its own PA value. Bambu Studio handles this automatically if you have different filament profiles assigned to each slot with their own PA values.

This matters for multi-color prints where you’re mixing materials. PLA and PETG have very different ideal PA values — if you’re using a support material with different properties than your main material, both should have calibrated PA values.

For more on AMS setup and multi-material printing, see our AMS troubleshooting guide and multi-color printing guide.

Pressure Advance Calibration Workflow (Quick Reference)

Here’s the step-by-step workflow I follow every time I put a new filament type on one of my production printers:

Load the filament and let it reach temperature
Run a temperature tower (or use known-good temperature)
Calibrate flow rate using the cube method
Run PA calibration in Bambu Studio (Calibration → Pressure Advance → Line Method)
Evaluate the results with good lighting and magnification
Set the PA value in the filament profile
Print a test piece with sharp corners (a calibration cube works great)
Verify corners are clean and crisp
Save the filament profile with a descriptive name
Add the PA value to my filament database so I don’t have to re-calibrate next time

This entire process takes about an hour per filament. It’s a one-time investment that pays off on every single print you make with that filament going forward.

What Pressure Advance Can’t Fix

PA is powerful, but it’s not a magic bullet. Some print quality issues that look like PA problems are actually caused by other things:

Ringing/ghosting: That’s a motion system issue, addressed by input shaping. See our input shaping guide.
Z-seam artifacts: Partly PA, partly slicer seam settings, partly retraction tuning.
Elephants foot (first layer bulge): That’s first layer squish / bed temperature related, not PA. Check our first layer calibration guide.
Stringing: That’s retraction and temperature, not PA.
Layer inconsistency: Could be wet filament, inconsistent temperatures, or mechanical issues.
General blobbing everywhere: Likely over-extrusion (flow rate too high) rather than PA. Calibrate your flow rate first.

Why This Matters for Production

If you’re printing for fun, default PA values are probably fine. Your prints will look good enough and nobody’s grading them.

But if you’re running a print farm — selling parts, making products, fulfilling orders — calibrated PA is the difference between “handmade 3D printed thing” and “this looks like it came from a factory.” Customers notice the quality. They feel the corners. They see the blobs.

At ADP Industries, every filament that goes on our production line gets the full calibration treatment. PA, flow rate, temperature, retraction. It takes time upfront, but it means every part that comes off our printers is consistent and professional. That consistency is what turns one-time buyers into repeat customers.

If you’re thinking about scaling up to a print farm, build calibration into your workflow from day one. Your future self will thank you.

Final Thoughts

Pressure advance calibration is one of those things that separates casual 3D printing from precision manufacturing. The test takes 15 minutes to print. The evaluation takes 5 minutes. Setting the value takes 30 seconds. And the payoff is visible on every single print you make going forward.

If you’ve never calibrated PA on your Bambu Lab printer, do it today. Pick your most-used filament, run the line test, and set the value. You’ll wonder why you didn’t do it sooner.

And if you want the complete calibration workflow — temperature, flow rate, PA, and retraction all dialed in — check out our other calibration guides:

Happy printing. And remember — the corners don’t lie.

Take Your Calibration Further

If you’re running a P2S or upgrading to the H2C Vortek, our paid guides go deeper than any free content — covering Develop Mode, per-material profiles, firmware-specific recovery sequences, and production-grade troubleshooting:

P2S Calibration Guide — $19.99 — 60+ pages for P2S owners
H2C Vortek Calibration Guide — $24.99 — Install + calibration playbook for Vortek upgraders