UV Mapping to a bitmap problem!

Hey everyone!

I’m trying to find a workflow from blender to Substance DESIGNER (not painter)and since SD can export bitmaps so, in my head, (i’m still learning) it works out like this :

  1. Modelling
  2. Unwrap it
  3. Exporting it as an .obj or .fbx and load it in on SD
  4. Texture the model in SD
  5. Export bitmaps
  6. Load PBR Shader in Blender and link images and done!

But I think I’m missing an important piece of the puzzle, the bitmaps are square and my UVs aren’t mapped correctly. Is it possible to make every and any UV map fir to a square? I’m so confused. Please help.