Infill Not Generating on Thin Walls  

Infill Not Generating on Thin Walls

I've been running into a weird issue with PrusaSlicer 2.7.1 on my MK3S+ running firmware 3.13.2. I'm trying to slice a fairly simple model that has a few thin vertical fins. The problem is that no infill is being generated for those parts, even when I crank the infill density up to 100% just for testing.

Setup:

• Printer: MK3S+
• Slicer: PrusaSlicer 2.7.1
• Filament: Prusament PLA
• Nozzle: 0.4mm
• Layer height: 0.2mm
• Infill: Grid, 100%
• Wall count: 2 perimeters
• Slicing profile: Standard 0.2mm PLA profile, minor tweaks to speeds and cooling

What I've tried:

• Bumped the wall count down to 1 → same issue
• Changed infill pattern → no difference
• Enabled Fill Gaps and played with advanced settings like Combine Infill Every → still no infill inside the fins
• Confirmed model is manifold
• Looked at the G-code preview layer-by-layer and confirmed nothing is being generated in the center of the fins—only perimeters

I want those thin sections to print solidly, or at least with some kind of fill instead of just empty shells. I know these areas are narrow, but at 0.8mm with a 0.4mm nozzle, I’d expect at least one internal line or an automatic fill.

Is there a slicer trick or setting I’m overlooking, or is this a known limitation/bug in how PrusaSlicer handles narrow geometry?