Hello I’m Ryxku and I’m in the UGC Program, I like making bundles and it’s very hard and long to make, and I notice a real bug sometimes when I make my own shading on blender. The normals are not the same than on Roblox Studio on a specific angle.
On Blender you can see all the faces are flipped correctly.
But when I import on Roblox Studio, the shading is correct but not all the normals. So there are a few holes :
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Thanks for the report! We’ll follow up when we have an update for you.
Hi @Ryxku!
I’m looking into this issue, but I have a couple of questions and suggestions for Immediate work arounds.
First Possibility:
This might be a winding order issue (In Roblox it’s not just the normal that used for backface culling, it’s the winding order [which is the way the vertices are actually stored]) you can check this by by turning the face orientation overlay on and making sure everything is the same color on each side
Good:
Bad:If this is the case you can just flip the inverted faces via the normal menu:
Second Possibility:
If you’re exporting as an .fbx file then there’s another issue that comes up occasionally while triangulating a face where it will fail to pick up the face and throw it out. Unfortunately because we use FBX’s built in triangulation code this isn’t something I can fix easily, but I can suggest some workarounds.
Pre-triangulate the face:
This might help because if it’s an issue with triangulation, and there’s nothing to triangulate for that particular face than it’ll never run into that issue. For flat faces it’s a pretty easy (if not ideal) task, and you can use the knife tool to split them up into triangles.
This will sometimes resolve the issue, and is worth a shot.
Export as glTF:
The other sure fire option to sidestep triangulation issues is to export as a .gltf or .glb file instead. Because glTF files are pre-triangulated it will look just as it does in blender. The only catch when switching from .fbx export is that the scale will be 1:1 with studs (vs. .fbx 1:100 scale) so you might need to change your export scale.
Hopefully one these can fix the issue!
If not feel free to DM me the specific geometry that’s having the issue and I can investigate further 
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Hey thank you for your answer, I’ll check if the second option works!
So I tried to triangulate as you said but it doesn’t fit at all my issues. Here an example this arm is not flipped correctly on Roblox, but it’s flipped correctly on Blender :
