UE 5.8 Edit Skin Weights – Relax causes clothing seams to split

Development Character & Animation
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UE 5.8 Edit Skin Weights – Relax causes clothing seams to split

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?

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Hey there! Welcome to the Unreal community

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.

Here are links that might help you:
Skin Weight Editing EditSkinWeights USkinWeightModifier

I would appreciate it if you could tell me about these extra details at any time!