Pillowing on Top Layers: Causes and Fixes

You finish a print and the top surface looks like a poorly made waffle — bumpy, uneven, with small dips or even holes where the surface dips into the infill gaps below. This is pillowing, and it happens when the top layers cannot bridge across the infill pattern underneath. It is one of the most common surface quality issues and also one of the easiest to fix.

Pillowing occurs because the top layers of a print are essentially bridging across the gaps in the infill. If there is not enough material, not enough cooling, or the gaps are too large, the top surface sags into the voids and creates that characteristic bumpy texture.

What Causes Pillowing

Three factors work together to create pillowing:

1. Not enough top layers — Each top layer covers the gaps below a little more. With too few layers, the gaps never fully close.
2. Insufficient cooling — If the filament does not solidify fast enough, it sags into infill gaps before the next layer can support it.
3. Infill percentage too low — Lower infill means larger gaps between infill lines, which means longer unsupported spans for the top layers to bridge.

Usually, fixing just one of these three eliminates pillowing entirely. Fixing all three guarantees a smooth top surface.

Fix 1: Increase Top Layers

This is the most reliable fix. Each additional top layer adds material that fills in the dips from the layer below. Eventually, enough layers stack up to create a fully smooth surface.

Recommended top layer count:

| Layer Height | Minimum Top Layers | Recommended | |---|---|---| | 0.3mm | 4 layers (1.2mm) | 5-6 layers | | 0.2mm | 5 layers (1.0mm) | 6-8 layers | | 0.12mm | 8 layers (0.96mm) | 10 layers | | 0.08mm | 12 layers (0.96mm) | 14 layers |

The rule of thumb is at least 1.0mm of top solid material, regardless of layer height. With 0.2mm layers, that is 5 layers minimum. With 0.08mm layers, that is 13 layers.

In your slicer:

• OrcaSlicer / PrusaSlicer: Top Solid Layers (or set Top Shell Thickness in mm)
• Cura: Top Layers under Shell settings

According to All3DP's pillowing guide, increasing top layers is the most effective fix because it addresses the root cause directly.

Fix 2: Increase Part Cooling

Better cooling solidifies the top layers faster, preventing them from sagging into infill gaps before they set.

Settings:

• PLA: 100% fan speed (should already be here — if not, increase)
• PETG: 60-80% on top layers (PETG tolerates more cooling on top layers than on walls)
• ABS: 20-40% on top layers if you can do so without warping

If your printer's stock fan is weak, upgrading to a more powerful fan makes a measurable difference. The WINSINN 4020 Blower Fan is a common upgrade for Ender-style printers.

A better fan duct also helps — search 3DSearch for fan ducts designed for your printer model.

Fix 3: Increase Infill Percentage

Higher infill percentage means smaller gaps between infill lines, which means the top layers have shorter distances to bridge.

Infill and pillowing relationship:

| Infill % | Gap Size | Pillowing Risk | |---|---|---| | 10% | Large gaps | High | | 20% | Moderate gaps | Moderate | | 30% | Small gaps | Low | | 40%+ | Very small gaps | Very low |

If you are printing at 10-15% infill and seeing pillowing, increasing to 20-25% may be all you need. You do not have to go to 100% — just enough to reduce the gap size below what your top layers can bridge.

Alternative: Some slicers offer gradual infill which increases infill density near the top surface without increasing it throughout the entire print. This gives the top layers more support without using extra filament in the middle.

• OrcaSlicer: Gradual Infill setting
• Cura: Gradual Infill Steps

Fix 4: Reduce Print Speed for Top Layers

Slower speed on top layers gives each line more time to bond with the layer below and more time for the cooling fan to solidify it.

Recommended top layer speed:

• 15-25 mm/s for problematic top surfaces
• This is slower than your regular infill or wall speed, but it only affects the last few layers, so the time impact is minimal

In your slicer:

• OrcaSlicer: Top Surface Speed
• PrusaSlicer: Top Solid Infill Speed
• Cura: Top Surface Skin Speed

Fix 5: Change Infill Pattern

Some infill patterns provide better support for top layers than others because they distribute their lines more evenly.

Best patterns for preventing pillowing:

• Gyroid — excellent top-layer support because the infill contacts the top layer at many points
• Grid — good support with perpendicular line crossings
• Cubic — 3D pattern that provides consistent support
• Lines / Rectilinear — alternating direction provides decent support

Worst patterns for top surface:

• Lightning — designed for support, not structural infill; leaves large gaps near top
• Very low-density tri-hexagonal — large open cells

According to CNC Kitchen's infill comparison, gyroid infill provides the most consistent support for top layers among common patterns.

Fix 6: Use Ironing

Ironing is a slicer feature that makes an extra pass over the top surface with the nozzle, essentially smoothing and filling any remaining imperfections. It does not fix severe pillowing, but it polishes out minor bumps and dips.

In your slicer:

• OrcaSlicer / PrusaSlicer: Enable Ironing in the quality settings
• Cura: Enable Ironing under the top/bottom settings

Ironing adds print time but creates a glass-smooth top surface when combined with adequate top layers and cooling.

Fix 7: Lower Nozzle Temperature

Lower temperature means the filament solidifies faster after extrusion, reducing sag into infill gaps. Try reducing by 5-10°C from your normal temperature.

Caution: Do not go so low that you cause under-extrusion or poor layer adhesion. Use a temperature tower to find the lowest temperature with good results.

Fix 8: Use a Smaller Layer Height

Smaller layer heights mean thinner layers, which cool faster and sag less. If you are printing at 0.3mm and seeing pillowing, try 0.2mm. The thinner layers bridge across infill gaps more easily.

This also means you need more top layers by count, but the same total top thickness (1.0mm+) applies.

Special Cases

Pillowing Only in the Center

If pillowing appears only in the center of large flat surfaces (not near the edges), the issue is that the center of the top surface is farthest from any supporting walls. The infill alone must support it. Increase infill percentage or use gradual infill.

Pillowing with Large Nozzles

Larger nozzles (0.6mm, 0.8mm) extrude wider, heavier lines that sag more easily. When using a large nozzle:

• Increase top layers by 2-3 beyond the standard recommendation
• Increase infill by 5-10%
• Ensure adequate cooling

Pillowing on Enclosed Printers

Enclosed printers like the Bambu Lab P1S have higher ambient temperatures inside the chamber, which reduces the effectiveness of the cooling fan. For PLA in an enclosure, consider opening the door or removing the top panel if pillowing is an issue.

Quick Fix Summary

If you are seeing pillowing right now and want the fastest fix:

1. Add 3 more top layers than whatever you have now
2. Set fan to 100% for PLA
3. If infill is below 20%, increase to 20%

That combination fixes pillowing in the vast majority of cases.

Recommended Print Settings to Prevent Pillowing

Top Layers: 6 (at 0.2mm layer height) / 1.2mm minimum thickness
Infill: 20% minimum (gyroid or grid pattern)
Cooling Fan: 100% for PLA, 60-80% for PETG
Top Layer Speed: 20 mm/s
Ironing: Enabled for critical surfaces

For printer-specific optimized settings, try the AI Settings feature on 3DSearch — search for your printer model and filament type.

Final Thoughts

Pillowing is a straightforward problem with straightforward solutions. More top layers, more cooling, and adequate infill density are the three levers. Pull any one of them far enough and pillowing disappears. For the smoothest possible top surfaces, combine all three optimizations and add ironing. The extra filament and print time are negligible, and the quality difference is immediately visible.