Holes or pillowing in the top surface
The top solid layer has gaps, or bulges upward between infill lines.
gaps in top layerrough topyou can see the infill
Causes, most likely first
Ordered by how often each is actually responsible, not by how interesting it is. Work down the list.
Not enough top layers
Use at least 4–5 top layers. Solid layers need something to span onto.
Infill density too low to support the top
Raise infill to 15–20%. Top layers are bridging across the infill gaps.
Not enough cooling on the top surface
Raise the fan for solid top layers so each bridged line sets before the next.
The app walks this in order, generates the test model for your nozzle and filament, and
records what you measure so nothing has to be repeated. Free, no account, works offline.