No commercial renderer implements true layering .. do you ?
There are many models :
drive.google.com/drive/folder...
Video is using a plain blend op :
Final = Base * (1 - Blend1) + Coat1 * Blend1 * (1 - Blend2) + Coat2 * Blend2 ...
Let's add a 'fresnel map' and call it phys based ! ;)
drive.google.com
Layered - Google Drive
