Hi, I’m using Edit Skin Weights in Unreal Engine 5.8.2 to fix the skinning of MetaHuman pants.
Whenever I use Relax/Smooth, the pants start splitting apart along the center seam and several other seams, as shown in the attached images.
Before using Relax, the pants are completely closed and animate normally. Undoing the Relax also closes the seams again.
I watched a tutorial where the same Relax workflow was used on pants without this problem.
What could cause Relax to separate the mesh along its seams, and how can I fix it?
Also, I’m mainly a 3D modeler, and my goal is to create complete MetaHuman clothing assets ready to sell on Fab. I’ve spent quite a lot of time trying to understand and fix skin weights inside Unreal.
For artists who have actually worked with MetaHuman clothing: do you prefer fixing/finalizing skin weights in Maya, or directly inside Unreal Engine? Which workflow has been more reliable for production-ready Fab assets?
I think what happens when you’re using Relax/Smooth is that it averages the weights of the split boundary vertices along the seams where the UVs or materials are split causing the vertices next to the seams to push away from each other
Can you give some context before I go any further?
Are the seams on your mesh physically split (UV seams/hard edges where vertices are duplicated) or is it a single continuous mesh?
When using the Edit Skin Weights tool, Do you have any specific brush settings toggled? (like Prune, Clamp or vertex selection modes)
Are you using Transfer Skin Weights from the base MetaHuman body mesh first or painting them entirely from scratch?
In the meantime if you’d like to test a quick potential fix in Unreal you could try to see if you get better results by locking boundary vertices or trying to relax using the Component Selection Mode (selecting vertices on both sides of the seam first)
Regarding your question about Maya vs. Unreal for Fabric:
While UE’s skinning tools have gotten really good in recent versions I think most character artists who need to do precise weight painting for Fab will still tend to do their final cleanup in Maya/Blender. It’s just easier to have full control over edge loops and welded vertices.
Relax is averaging weights across vertices that only look connected. On MetaHuman-style clothing the center seam (and most UV seams) is physically split: two vertices sit on top of each other but they are not the same vertex. The brush often hits only one of them, so those two drift onto different bones and the seam opens. Undo closes it because the weights go back, which matches what you are seeing. A tutorial mesh that stays closed is usually welded, or the brush happened to cover both sides.
What to do instead of Relax on that seam:
Get the base weights from the body, don’t smooth them on. In Edit Skin Weights use Transfer Skin Weights from the MetaHuman body mesh (small distance threshold, so only the coincident verts are matched). Coincident seam verts then receive the same source bone and the seam stays shut while the pants follow the legs.
If you still need to smooth a region, box-select both vertices of the seam (the two that share the position) before Relax, so they average toward the same result. A paint stroke that only catches one side will split it again. Keep the brush radius small and the strength low, and stay off the seam line itself.
After the transfer, only hand-paint the spots that clip (crotch, knees) with a low strength. If the garment is symmetric, mirror the weights instead of relaxing across the mirror line.
Prune / Clamp / a low Max Influences will make this worse on a seam, because the two verts can drop different bones and then normalize apart. Leave those off until the seam verts already match.
For a clothing asset you want to ship, treat Transfer-from-body as the default and Relax as a last step away from split edges. Welding the seam in a DCC just so Relax is safe will also weld the UV seam, so don’t do that if you still need the UV split; transfer the weights instead.