Soo, I explain mzself with a practical example. I am about to finish a project based on a Mill. After the modelling phase I thought the best thing to do before UV unwrapping was to separate the Mesh in its different parts (so for examples the arms of the Mill, the central wheel, the rings on the side, the screws and so on). I then UVunwrapped the different parts singularly (some of them required the use of seams, some were good to go with the smart project function) and then exported my Blender file as an .fbx, with all its UVmaps, to Substance Painter for the texturing phase. (This part can be totally wrong in terminology. I am not sure if in this process the UVmaps are actually exported or which role they are playing whatsoever). Everything fine in Substance Painter, even though I had many different objects since they were separated not only in the model but also with different materials. When I finished the texture phase in Substance Painter I imported everything back to Blender where I decided to put all of the pieces of the mill back together in order to do an animation. After doing so, even though the object looks as I want, I have noticed that the UV maps of the separate objects are now all together (overlapping like crazy) and it seems to me that, even though it causes no apparent problem, that is not the good way to go. Plus, after this separating-putting-back-again the parts the model is not so clean. I feel as if I am totally missing comprehension on what is the meaning of UVmaps and materials, how they interact with one another (specifically in the case of future editing of the model) and above all what is the best workflow to model something in Blender, moving it to Substance Painter after having unwrapped it and going back to Blender without any issue and with the most efficiency. 
I couldn’t find much resources about this on the internet, I am very open for your suggestions, opinions and hints on what is a good workflow or which resources should I read to understand such things.

If the question is not too clear I can reformulate it, in such case please just ask.

Thanks in advance


1 Answer 1


You're quite close to the correct workflow: UV maps are a flat projection of the 3D mesh, where every face gets mapped into a 1 x 1 square (or rectangle), meaning that every UV vertex gets a value X (U) between 0 and 1 and a value Y (V) between 0 and 1.

UV maps travel with vertices, they are simply 2 numbers (U and V) that define a location into a square, every vertex gets a UV coordinate, when exporting this coordinate gets exported too.

Every material rely on a UV map to correctly place textures: as soon as materials are different they don't get problems from overlapping UVs.

Every mesh can have multiple UVs, in the shader editor you can add a UV map node to choose which UV map will use the material (without an UV node the first UV map in the list gets used by default).

So, after joining the mesh you can add a new UV map using the + button (it will be a copy of the overlapping UV) then in a UV editor you can select all UV islands one by one and move and scale them so that no overlap occours (give more UV space where more details are needed, give less UV space where there are flat colors and less details).

Then create a new material, assign to it the new UV map and bake all textures one by one.

Then you can delete all others materials and UV maps and use the new ones for the whole model, with a single non overlapping UV map and a single set of textures.

Last professional touch can be store greyscale textures into a single channel of an image (i.e. Roughness into Red channel, Metalness into Green, AO into blue).

This workflow is a good habit, it becomes essential if you will export your model to others softwares, expecially game engines. If you remain in Blender - Substance Painter don't worry about overlapping UVs, they're fine as soon as materials are different.

  • $\begingroup$ Thanks for the answer. I was still missing the part of "Every material rely on a UV map to correctly place textures: as soon as materials are different they don't get problems from overlapping UVs". But what I still don't understand is what, how can one pack all the different parts of an object into the same UVmap in order to have only one instead of many? Maybe by grouping the different objects? What I think would be the best is to have an object with its many parts but with only one UVmap (or two maximum) but to unwrap the single parts separetely in order to choose the best way in each case. $\endgroup$
    – Fabio95
    Commented Jan 21, 2022 at 9:15
  • $\begingroup$ The procedure I describe "after joining the mesh ...." is exactly how to obtain a single material with a single UV Map and a single set of textures for any complex object. $\endgroup$ Commented Jan 21, 2022 at 12:25

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