> For the complete documentation index, see [llms.txt](https://ronanmahon-art.gitbook.io/pbr-check/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://ronanmahon-art.gitbook.io/pbr-check/why.md).

# Why?

<figure><img src="/files/te9NSLPw9nZbqeyiQqxU" 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)