For Milkroom Studios I implemened Xrite's CarPaint model in axf 1.2.
While there is an axf implementation for Unreal, it lacks the car paint model, and for good reason: The shader represents existing car paints using multiple lobes, color tables and an array of flake textures (usually >60 textures), all based on real measurements.
While the the shader is very well documented, it was a challenge to get it working in Unreal, since it requires a custom version supporting texture arrays. Since the shader is incompatible with Unreals IBL, lights are set according to a 360° image using the Median Cut algorithm.
A big thank you to Gertrud Gottlieb who was my partner in crime for this project and helped with dissecting the physics involved, and to Gero Müller, one of the heads behind the axf format, for patiently answering our questions.