Retopology in Blender for AI-Generated Meshes

Prerequisites

• A GLB or FBX from your generator, imported (importing AI 3D models into Blender).
• Real-world scale already set, so the voxel size you choose means something physical.
• A target triangle or quad count from your engine’s limits. We know of no engine that publishes a universal figure; see the cleanup hub for what is documented. Keep the units straight: an all-quad mesh has twice as many triangles as faces, so 10,000 quads is about 20,000 triangles.

Why voxel first, then quads

The two remeshers do different jobs, and the Blender manual says so directly. The Voxel remesher places the mesh in a grid and creates a new surface, which has uniform topology and no inner self-intersecting geometry. The Quad remesher, which runs QuadriFlow, can produce better results but is slower, and “it’s not a replacement for the Voxel remesher” because it does not clean up intersecting geometry. For a shell that may be full of overlaps, voxel takes care of the surface and QuadriFlow takes care of the layout.

The manual also warns off some uses. It says not to use voxel or quad remeshing to reduce the face count of a mesh that otherwise has no geometry problems (use Decimate), and not for final topology on a deforming character. If your AI mesh is already sound, skip this page and decimate instead.

Steps

1. Duplicate the mesh and hide the original. This copy is your bake source later. Voxel Remesh, per the manual, will “lose all mesh object data layers associated with the original mesh” (UVs included), so never remesh your only copy. Why it matters here: the generator’s texture is tied to its UVs, and the remesh deletes them.
2. Clean the shell in Edit Mode. Use Mesh > Clean up: Delete Loose, then Merge by Distance (set Merge Distance small), then Fill Holes (the Sides option; 0 fills all). StraySpark says QuadriFlow wants a closed surface and that hundreds of open shells are the opposite of that, so cleaning first is the safer order. For finding and removing whole floating pieces and for what each operator does, see repairing holes, floaters and broken pieces.
3. Apply anything you need to keep. The manual says remeshing works only on the original mesh data and ignores modifiers and shape keys, and that it is not possible on objects with a Multiresolution modifier. Apply or remove those first.
4. Voxel remesh. You have two routes to the same tool. In Object Mode, use Properties > Data > Remesh with Mode set to Voxel, which offers Voxel Size, Adaptivity, Fix Poles and Preserve (Volume, Attributes). Or in Sculpt Mode, open Tool Settings > Remesh (or Sidebar > Tool > Remesh), set Voxel Size (pressing R shows the size as an overlay; holding Shift gives finer control), then press Voxel Remesh (Ctrl-R); there, Sample Voxel Size picks a size from an area of the mesh, and Preserve lists Volume, Paint Mask, Face Sets and Color Attributes. Leave Adaptivity at zero unless you want it: the manual says any value above zero disables Fix Poles and can introduce triangulation. Blender 5.2’s release notes say the voxel remesher now interpolates vertex and corner attributes, and present that as better preservation of vertex paint. They do not say UV maps survive, so plan on new UVs.
5. Choose a voxel size. The manual gives no formula. StraySpark, which sells a competing cleanup add-on, published an empirical one: dense = target_tris × (2 + 4 × quality), voxel_size = 0.9 × bbox_diagonal / √(2 × dense), with quality 0.5 by default. They describe the 0.9 as empirical. Treat it as a starting guess and adjust by eye.
6. QuadriFlow. With the voxel-remeshed object selected, go to Properties > Data > Remesh, set the mode to Quad, and click Quadriflow Remesh, which opens a pop-up. Options per the manual: Use Mesh Symmetry, Preserve Sharp, Preserve Mesh Boundary, Preserve Attributes, Smooth Normals, a Mode of Ratio, Edge Length or Faces, and a Seed. Use the Faces mode if you have a hard budget. If the layout is poor, try another Seed: the manual says different seeds give different quad layouts.
7. Check what was lost. StraySpark says a voxel grid cannot represent anything thinner than one voxel, naming straps, antennae, cloth edges and fingers as features that can fuse or disappear. Compare against the hidden original. If thin parts matter, shrink the voxel size and accept a higher intermediate count, or retopologize those parts by hand as described below.
8. UVs. The remeshed mesh has none. In Edit Mode choose UV > Unwrap > Smart UV Project and adjust Angle Limit and Island Margin in the Adjust Last Operation panel. More options on UV and texture fixes.
9. Bake. Transfer color and normal detail from the hidden original onto the new mesh: baking normal maps from a high-poly AI mesh.
10. LODs. Build them from this final mesh: LODs for AI-generated models.

Worked example: a starting voxel size

The inputs are invented to show StraySpark’s formula, with a default quality of 0.5. A prop with a bounding-box diagonal of 2.0 m and a budget of 20,000 triangles:

• dense = 20,000 × (2 + 4 × 0.5) = 80,000
• √(2 × 80,000) = 400
• voxel_size = 0.9 × 2.0 ÷ 400 = 0.0045 m, or 4.5 mm

Anything on that prop thinner than about 4.5 mm is at risk of the fusing StraySpark describes, so compare a strap or an antenna against the original before moving on.

Doing the deforming parts by hand

Automatic topology will not give you edge loops around a joint or a mouth, so anything that bends needs manual retopology, either from scratch or on top of a QuadriFlow base. The manual’s method is to create a new mesh that overlaps the original, then adjust it until it fully covers the original and matches its shape.

1. Set up the display. In the 3D Viewport’s Overlays, turn on Retopology. It makes the edited mesh see-through so the sculpt shows beneath it, and its Offset moves the edited mesh toward the camera for display. The manual prefers this to X-Ray because it avoids distracting geometry on the far side.
2. Set up snapping. Enable snapping and set Snap Target to Face, which the manual singles out as useful for retopologizing. Shift-Ctrl-Tab opens the options. Target Selection has Backface Culling to stop vertices sticking to the far side. Under Snap Target for Individual Elements, Face Nearest also allows snapping to occluded geometry, unlike Face Project.
3. Draw with Poly Build. Choose Toolbar > Poly Build in Edit Mode. Per the manual: Ctrl-LMB adds a vertex and face to the nearest edge, Shift-LMB dissolves or deletes, dragging a vertex moves it, and dragging an edge extrudes it into a quad. Create Quads dissolves the shared edge so new triangles become quads. Auto-merge while tweaking helps combine vertices.
4. Halve the work on symmetrical meshes. The Mirror modifier has Axis, Clipping, Merge and Bisect options. Build one side.
5. Inspect. Select > Select All by Trait > Poles by Count finds vertices with an unusual number of edges, and the manual notes these can pinch under Subdivision Surface.

Shrinkwrap is practitioner method, not manual procedure. The manual’s retopology section describes snapping and does not mention Shrinkwrap. Tutorials from RebusFarm and Fox Renderfarm do, commonly adding the modifier as a safety net. If you use it, the documented fields are Target, Wrap Method (Nearest Surface Point, Project, Nearest Vertex, Target Normal Project), Snap Mode (On Surface, Outside Surface, Above Surface, Inside, Outside) and Offset.

What goes wrong

When to stop

Stop when the silhouette matches the original at the distance the camera will see it, the count meets your engine’s documented limit, and the baked asset looks right in the engine. Further topology polish rarely shows on props. If you are weighing paid tools instead of this free route, see Blender retopology add-ons compared.

Not verified

The manual’s Remesh modifier page lists no Voxel Size field, so this page uses the Data panel and the Sculpt Mode tool. The manual’s description of Preserve Mesh Boundary reads oddly (it talks about volume, the same wording as Preserve Volume); possible documentation error. Screen recordings are planned but do not exist.

This page is part of the Cleaning Up AI 3D Models section.