ROUGH OR PILLOWING TOP SURFACE

The top surface of a print is bumpy, wavy or has visible holes between infill lines instead of being smooth and closed.

Your top surface is a series of bridges over infill. Each top layer line is unsupported between the infill walls below it and has to solidify before gravity pulls it down into the gap. If there is not enough material to span the gap, not enough cooling to freeze it in place, or not enough subsequent layers to flatten the bridging texture, the bumps remain visible all the way to the surface. The number of top layers compounds. The first top layer bridges actual infill gaps and sags. The next layer bridges the sag from the first layer. Each additional layer flattens out the previous one a bit more. With only two or three top layers there isn't enough thickness to ever fully smooth out, so the original infill geometry shows through forever. Cooling is the second multiplier. A part fan running at 100% on PLA freezes each tiny bridge in place before it can sag, while a fan at 30% lets the same bridge droop visibly. PETG and ABS have lower cooling tolerance, which is why they consistently produce rougher tops than PLA at default settings.

Based on 355 confirmed fixes from r/FixMyPrint, these are the causes ranked by how often they actually worked: 1. Not enough top layers - the most common confirmed fix. Going from 3 top layers to 5-7 (or to a 0.8-1.0 mm minimum top thickness) solved most cases. 2. Infill too sparse - raising from 10-15% to 20-25% gave subsequent top layers enough support to bridge cleanly. 3. Top surface speed too fast - dropping the dedicated top-surface speed to 20-30 mm/s while leaving normal print speed alone fixed many cases without slowing the whole print. 4. Cooling fan too low for top layers - cranking part cooling for the top surface (some slicers expose this separately) closed up small holes. 5. Ironing not enabled - on otherwise dialled-in printers, enabling ironing took an already-good top surface from acceptable to mirror-smooth. Data sourced from r/FixMyPrint - one of the largest 3D printing troubleshooting communities on Reddit. This represents real user-reported issues and community-confirmed fixes, not theoretical advice.

If you can see straight infill lines through the surface texture - top layer count is too low. The geometry below is bleeding through. If the surface has small holes or gaps that look like missed lines - infill density is too low and top layers are sagging into the gaps. If the surface is closed but covered in fine ripples or bumps - top surface speed is too fast or the part fan is too slow. If the bumps are larger and more random - this is likely wet filament instead of pillowing - check for popping sounds during printing. If only the centre of large flat tops is rough - this is classic pillowing from inadequate top thickness over wide infill spans. Add more top layers or use ironing.

Cause 1: Not enough top layers Set top layers to at least 5 and set top minimum thickness to 0.8-1.0 mm. Use both. At 0.2 mm layer height, 5 layers gives 1.0 mm. At 0.12 mm layer height, you'll need 7+ to reach 0.84 mm. Cura: 'Top Layers' + 'Top Thickness'. PrusaSlicer/OrcaSlicer: 'Top solid layers' + 'Minimum top shell thickness'. Bambu Studio: 'Top shell layers' + 'Top shell thickness'. Cause 2: Infill too sparse Raise infill density to 20-25%. The relationship is not linear - 10% to 20% is a huge jump in top quality, 25% to 50% barely changes anything for surface finish. Use Gyroid or Cubic infill - both support top layers more evenly than Lines or Grid. Cause 3: Top surface speed too fast Set top surface speed to 20-30 mm/s as a separate setting from your overall print speed. This adds maybe 1-2 minutes to a typical print and dramatically improves top quality. Cause 4: Top layer cooling too low PLA: 100% on top layers. PETG: bump from your normal 30-50% to 70-80% on top surfaces. ABS/ASA: 30-50% on top surfaces only (still risky to crank up overall fan but the top surface is forgiving). Cause 5: Enable ironing Ironing runs the nozzle over the finished top at near-zero flow to flatten remaining bumps. Speed 15-25 mm/s, flow 5-15%, inset 0.2 mm. Adds time but produces a near-mirror finish. Don't use ironing as a fix for severely pillowed tops - fix the underlying cause first.

Bowden printers (Ender 3 family): Ironing works but is slower because lower acceleration limits ironing speed. Worth it on display pieces only. Make sure the cooling fan duct is intact and aimed properly - many stock Ender 3 ducts blow past the print rather than at it. Direct drive printers (Bambu, Prusa MK4S): Ironing is fast and produces excellent results because of higher acceleration. Bambu Studio has 'Ironing speed' and 'Ironing flow' easy to adjust. Default ironing settings on Bambu are usually too aggressive on flow - drop to 8-10%. Enclosed printers (Bambu P1S, K1 Max): Top surface fan needs to be higher than open-air printers because the chamber traps heat. PLA top surfaces in an enclosure can pillow even with the fan at 100% - consider venting the chamber for prints with lots of flat top surface.

PLA / PLA+: The easiest filament for clean top surfaces. Max fan, 5 top layers, ironing optional. Achieves mirror finishes with no special tuning. PETG: The hardest filament for clean tops. PETG bridges poorly which makes top layers prone to pillowing. Use 6-7 top layers, 25% infill, top surface speed 25 mm/s, top fan at 70-80%. Skip ironing - PETG ironing produces clear strings that ruin the finish. ABS / ASA: Good top surfaces if you have enough layers (6+). Use 30-50% fan on top surfaces only. Ironing works well on ABS in an enclosure. TPU: Notoriously difficult top surfaces because TPU doesn't bridge well. Use 7+ top layers and 30%+ infill. Ironing TPU does not work - it just stretches.

Set your slicer profile defaults to 5 top layers and 20% infill minimum. Anything less is a constant source of mediocre top surfaces. Add a separate top surface speed of 25-30 mm/s to your profile. The marginal print time increase is worth it for every flat-topped print you'll ever make. For display pieces, enable ironing as a saved option. For mechanical parts, skip ironing - the time saved matters more than visual finish.

Use FixMyPrint to get top layer count, infill density, top surface speed and ironing values tuned for your specific printer and filament - based on what actually worked for similar issues in the community. Go to /settings-generator to generate yours.