Why?

Unreal’s PBR system requires specific base color and metallic ranges

Base Color	Material Result
Value too dark	weak material response & low light bounce
Value too bright	washed-out highlights & high light bounce

Metal materials

Base Color	Material Result
Value too dark	above plus no visible surface reflections

Key PBR Ranges

• Materials should generally be either non-metal (0) or metal (1)

• Metallic values between can work in transition areas, like raw metal blending into rust.

• There’s no single “correct” roughness value—materials vary, often within themselves.

• Materials that are fully smooth or rough are flagged to help catch accidental values of 0 or 1, or where more variation might be needed.

Further reading

If you want to know more about Physically Based Rendering, these great resources will help:

The PBR Guide Physically Based by by Anton Palmqvist Physically Based Materials in Unreal Engine