Abdomen Area Glitch Problem on Fat Sim

Hi. The skirt is just not adapted the way it should be. Pretty much everything needs to be re-done
- Skirts and legs behave differently in game. For your skirt to behave as intended, it must receive data from a skirt of similar length. Your reference is shorter, so a portion of it received data from legs.
- All parts of the body covered by clothing must be deleted, otherwise they serve no purpose and there is a high chance they will clip into your garment, which is what is happening in your case;
- Another thing that serves no purpose is adding the inner side where you cannot see it. It will cause you problems during baking;
- When it comes to vertex painting, there is a different hex code for skirts. It is always best to just transfer vertex paint;
- the skirt received no uv_1;
- when you assign rectangular textures to uvs, generated in the square uv space, they stretch vertically. If you wont bring them back, any pattern will be distorted.

Before i'll write how to fix these issue, tell me, can your computer run blender 4.1?

To preface, your garment is made in a way it shouldn't be. You won't find a single maxis item with deep folds like this because they move oddly and the bottom is difficult to close.
So the process of making this skirt work will not be easy. If this is your first ever item, i would advice you to learn the cc making progress on something that is simple and doesnt have obstacles that you would need to put extra efforts to overcome.

But anyway:
- open your MD file of the skirt, select all patterns, Property editor - Miscellaneous - Mesh type - Quads, Simulate;
- then increase Particle distance, stopping just before the mesh starts looking like crumpled paper;

- export the mesh as thin and weld, without the avatar, close MD;
- download and install blender 4.1 in the recommended location or on the d drive;
- in s4s settings change blender path blender.exe in blender 4.1 installation folder;
- choose a maxis skirt of similar length ( can be longer but not shorter ) and with as little sculpted details as possible. For example, yfBottom_EF11SkirtPencil. Clone this skirt, export the blend, open;
- in 3d view select the skirt and rename the meshgroup to Reference. Delete the other two meshgroups;
- import your skirt;
- in uv editor Alt-click to select the top edge loop, Edge - Mark sharp, then press F. Uv- Unwrap, put that uv island somewhere to the side. Dont close the hole at the bottom or add the other side yet;
- transfer weights, uv_1 and vertex paint as shown below;

- hide the reference;
- expand the rig, make bottom visible and selectable. Select it, in 3d view press Shift D, then Esc to duplicate. Hide bottom;
- select bottom.001, switch to Edit mode, select everything with A, Mesh - Merge - By distance. Enable X-ray. At this point you would delete everything covered by the garment. In this case, delete the groin only;
- in this order: select bottom.001 first, Ctrl-select the skirt, join with Ctrl J;
- select uv_0, select uvs of the skirt, assign a template, press S Y 0.5 to brings uvs back to their original space. Put them in free space. Scale all uvs uniformly so that there is no difference in their quality. Bigger uvs = better quality;
- with Skirt's uvs selected, UVs - Export uv layout, set opacity to 0;
- once done, assign 0000 cut, save;
- filter the catalog by 1 meshgroup, clone a skirt, import your blend, then a layout into diffuse, make other maps blank, check how it behaves;
- i did and the legs clip a bit in the front. However, im using the current version of the mesh, hopefully the retopologized one would behave better. If not, just move legs further away from the skirt with proportional editing;
- once happy with how the mesh behaves, select a visible portion of the skirt, press Shift D, Esc to duplicate, Mesh - Normals - Flip normals to change direction, then press Alt Shift and type 0.0002 to offset. Press Shift H to isolate. Select the top edge loop, mark as sharp, close with F, then unwrap. In UV editor move duplicated uvs away from original ones. You can make them smaller. Unhide everything with Alt H;
- Add Edge split modifier, disable Edge angle, apply;
- save and import back, check if anything clips. If the geometry that covers the hole does, delete it;
- now bake textures.

Here

- open s4s settings, change blender path to blender.exe (not blender-launcher.exe) in the installation folder of blender 4.1;
- clone a skirt and export a new blend (important), open it;
- check if s4studio mesh tools appeared;
- if yes, delete the original skirt, File - Append - the blend with your skirt - Object - the skirt meshgroup;
- assign the right cut, save, import back into the package