Too-thin to print.

Flags every painted patch narrower than one nozzle line — the slicer silently drops these at print time, so they print as the colour underneath. They light up in your chosen highlight colour so you can fix them before export.

Merge thin patches is a bulk fix: each too-thin patch folds into the colour it shares the longest edge with — what the slicer would do anyway, but now you can see it first. Undo-able.

• Always before exporting, when a patch could be too narrow to survive slicing.
• After Brush work where small details might be thinner than a nozzle line.
• After Magic Fill work on tightly subdivided meshes (lots of long thin slivers).
• Before sending a paid job to print — this catches the silent slicer-drop class of failure.

1. Check tab → Too-thin to print. Set Nozzle line width to your nozzle line (default 0.42 mm matches a 0.4 mm nozzle).
2. Toggle Highlight too-thin patches. The thin patches light up across the model (red by default).
3. Set the Highlight colour if red clashes with your model — pick a swatch (red, cyan, yellow, magenta, green) or set a custom colour.
4. Fix one by hand: switch to Grow, click a highlighted patch, it widens.
5. Fix all at once: click Merge thin patches. Every too-thin patch folds into the neighbour it shares the longest edge with.

• Wrong nozzle line width means flagging the wrong things. 0.42 mm matches a 0.4 mm nozzle; change it for 0.6 mm or 0.2 mm setups.
• Merge thin patches eats fine details if those details are narrower than your nozzle. By design — the slicer would have eaten them anyway. For finer detail, use a smaller nozzle.
• Highlight colour clashing? If it's invisible against your paint, you'll miss patches. Pick a swatch that pops, or set a custom one.