ZBrush Tip: Preserve UVs When Merging SubTools in ZBrush

Merging multiple SubTools into a single mesh can be safe for UVs if you follow a precise order of operations and avoid topology-altering steps. Here’s a reliable workflow to keep UVs intact and production-ready.

• Audit UVs before merging
  • For each SubTool, verify UV integrity with Tool > UV Map > Morph UV and Texture Map > New From UV Check.
  • Ensure UVs do not overlap across the parts you intend to unify in a single texture set. If they do, repack to non-overlapping 0–1 or plan a UDIM layout in your DCC before merging.
  • Optionally run Tool > Polygroups > UV Groups to create a PolyGroup per UV island (handy for ID maps and material assignment post-merge).
• Protect subdivision history (crucial for UV safety)
  • UVs live on the base (lowest) subdivision. If ZBrush forces you to delete lower subdivs during merge, you risk losing or desynchronizing UVs.
  • For every SubTool, go to the lowest subdivision level before merging. The ZPlugin > SubTool Master can set all visible SubTools to their lowest level in one click.
• Use the right merge method
  • In Tool > SubTool > Merge, disable Weld before Merge Down or Merge Visible. Welding may fuse vertices and change topology, which can invalidate UVs and vertex order.
  • Merge at the lowest subdivision level for all SubTools to avoid prompts that delete lower levels.
  • After merging, confirm that original PolyGroups are preserved (they typically are). If not, regenerate with UV Groups or Group Visible.
• Post-merge verification
  • Run Morph UV again and inspect seams. Watch for stretching or unexpected overlaps.
  • If each part previously used its own texture, remember a single merged Tool supports one active texture at a time. Consider baking consolidated maps with ZPlugin > Multi Map Exporter.
  • Create an ID map from PolyGroups to reassign materials quickly downstream.
• When not to merge internally
  • If you only need a single-file delivery (game engine, DCC) but want to keep SubTools separate in ZBrush, use ZPlugin > FBX ExportImport and export with merge options enabled. UVs and material assignments are preserved on export without changing your ZBrush scene.
  • Avoid Dynamesh, Boolean “Make Boolean Mesh,” Remesh, or ZRemesher if UVs must be preserved. These regenerate topology and wipe UVs; do them prior to UV work, then re-unwrap and rebake as needed.
• Extra safeguards and pro tips
  • Pack UVs per part into unique tiles (UDIMs) before merging if you need high texel density across many components.
  • Use Multi Map Exporter to bake normal, displacement, AO, and polypaint-to-texture after merging; enable “Use Multiple Tiles” if working with UDIMs.
  • Keep a pre-merge version of your Tool. If anything shifts, you can revert and iterate quickly.

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