# Why?

<figure><img src="https://308152196-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FoaMX32sQggfi8k6I5PGW%2Fuploads%2FSivzTJDdjrNgVeLCjPRa%2FRange.jpg?alt=media&#x26;token=44201045-1cb7-4b13-845f-0090580b75c5" alt=""><figcaption></figcaption></figure>

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](https://www.adobe.com/learn/substance-3d-designer/web/the-pbr-guide-part-1)\
[Physically Based](https://physicallybased.info/) by by Anton Palmqvist\
[Physically Based Materials in Unreal Engine](https://dev.epicgames.com/documentation/en-us/unreal-engine/physically-based-materials-in-unreal-engine)


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