# How are Specularity and IOR linked?

**URL:** <https://forums.unrealengine.com/t/how-are-specularity-and-ior-linked/405956>\
**Category:** Rendering\
**Tags:** refraction, PBR, unreal-engine, specular, Rendering, question\
**Created:** [October 2, 2017, 7:19am UTC](https://forums.unrealengine.com/t/how-are-specularity-and-ior-linked/405956 "2017-10-02T07:19:47Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![anonymous\_user\_81aa7c82](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@anonymous\_user\_81aa7c82](https://forums.unrealengine.com/u/anonymous_user_81aa7c82)\
**Post date:** [October 2, 2017, 7:19am UTC](https://forums.unrealengine.com/t/how-are-specularity-and-ior-linked/405956/1 "2017-10-02T07:19:47Z")

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Hi everyone

I recently read this presentation:

> **[Real Time Rendering](https://jesshiderue4.wordpress.com/real-time-rendering-an-overview-for-artists/)**
>
> A brief overview of the Real Time Rendering pipeline found in most game engines, and how it impacts the art you create.

In it, there is a section that relates specular to index of refraction.  
Quote: _The only times you should change specular is to control the index of refraction for very specific cases like ice, water and skin._

I don’t understand the relation at all.  
Could someone please explain that?

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**Author:** ![Deathrey](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Deathrey](https://forums.unrealengine.com/u/Deathrey)\
**Post date:** [October 2, 2017, 4:14pm UTC](https://forums.unrealengine.com/t/how-are-specularity-and-ior-linked/405956/2 "2017-10-02T16:14:17Z")

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Index of Refraction defines material’s specularity at normal incidence.  
Specular material input allows your to control the IOR in a more or less artist-friendly manner with a values from 0 to 1.

Default specular value roughly corresponds to IOR of most dielectric materials, so in most cases, you do not need to touch it. The exceptions are materials with high IOR, like gemstones(ruby,sapphire, various crystals etc). You would want to crank up specular on those.  
You mentioned water and ice and skin. These ones are quite close to default specular value, and you can safely leave specular unconnected for those. Last but not least, you can use specular control to reduce specularity in crevices/cavities.

Please note, that IOR input for translucent material’s refraction is completely separate thing, that has no effect on shading.