VRChat/Substance Painter

Substance Painter is great software for painting textures and baking AO. However, getting it to work with Unity can be a massive pain in the ass.

Substance Painter
Software

MSRP
USD $150
Sellers
$149.99

So, here's how.

Exporting From

Blender

Install CATS.
Ensure you've tweaked the UV atlas as best you can, as you will be unable to use the Auto-Unwrap feature in Substance (rigs get nuked).
Export as an FBX using CATS.

Importing Meshes

Open Substance.
Select File > New...
1. Select the Unity HD Render Pipeline (Metallic Standard) template. A pipeline for specular is apparently missing.
2. Select the FBX or OBJ you want.
3. Set Document Resolution to as much as your PC will suffer. I personally use 4096 for everything.
4. Make absolutely certain you're using OpenGL Normal Map Format.
5. If your atlas is screwed up and you're OK with nuking rigs/etc, go ahead and check Auto-Unwrap.
  - Seams: Will automatically recalculate all seams if set to Recompute All. Recommend leaving this on Generate Only Missing Data unless the model is turbofucked.
  - UV Islands: UV Islands are the chunks of mesh thrown onto the atlas. This setting affects whether Substance will automatically re-generate islands (Recompute) or use existing ones.
  - Packing: Packing is how well the islands are crammed onto the atlas so they all fit. Substance does an excellent job with this, so if you can, Recompute all. (Don't use for anything with rigging)
6. Smack OK and wait.
Important: Press CTRL+SHIFT+B to bring up the baking window. so you can bake AOs and normals. These are used in Smart Materials.
1. In Common Settings:
  1. Change Output Size to something like half of your document resolution. (2048 in 4096 documents, etc)
  2. Change Antialiasing to as high as your computer will suffer. I use Subsampling 8x8. This will significantly impact baking time.
  3. Change Match to By Mesh Name so you get fewer weird ray-tracing issues caused by intersecting with clothing or whatnot.
2. Hit OK to Bake. Go grab a coke.