I have never used Substance Designer, so I’m basing this off of looking at example files.

The SBSPRS files are XML that appear to specify the list and type of parameters used in the SBSAR substance.

The SBSAR file is just a 7-zip file. It expands to:
./assemblies
./assemblies/content
./assemblies/content/0000
./assemblies/content/0000/icon1234567890.png
./assemblies/content/0000/Example.xml
./assemblies/content/0000/Example.sbsasm

The Example.xml file appears to describe the inputs of the node, the outputs of the node, gui layout for the node, and presets to choose for the node.

The Example.sbsasm file starts with the magic word 5342 414d, which are the ASCII values for SBAM. Beyond that, I haven’t figured anything else out about it.

I was hoping that this would be compressed formats, XML, JSON, and/or IFF all the way down.