# Correct value of Specular for PBR Materials

**URL:** <https://forums.unrealengine.com/t/correct-value-of-specular-for-pbr-materials/487741>\
**Category:** Rendering\
**Tags:** PBR, shading, unreal-engine, specular, question\
**Created:** [August 23, 2021, 9:35pm UTC](https://forums.unrealengine.com/t/correct-value-of-specular-for-pbr-materials/487741 "2021-08-23T21:35:38Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![Viduttam](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Viduttam](https://forums.unrealengine.com/u/Viduttam)\
**Post date:** [August 23, 2021, 9:35pm UTC](https://forums.unrealengine.com/t/correct-value-of-specular-for-pbr-materials/487741/1 "2021-08-23T21:35:38Z")

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Hi all,

I am new to UE4 and come from a Film/VFX background having worked on several offline render engines such as Renderman, Arnold, Vray, Mantra.

**I have a question pertaining to creating PBR Materials in UE4**

As per the UE4 documentation for [PBR Materials](https://docs.unrealengine.com/4.27/en-US/RenderingAndGraphics/Materials/PhysicallyBased/), it says the default specular value for say plastic should be set to **0.5** (Refer the Specular section - Table of Measured Specular Values)

However, if I scroll down on that same page to the References and open up the first reference link which points to the [blog from Lagarde](https://seblagarde.wordpress.com/2011/08/17/feeding-a-physical-based-lighting-mode/), it states that for PBR materials, specular values are actually fresnel reflectance at normal incidence i.e. f0. Which means for most plastics and dielectrics, the specular value will be **0.04** (based on IOR of 1.5). Additionally this page also has a table for specular values for different PBR materials.  
Now this specular = f0 theory is what is used in almost all offline render engines for PBR materials

As per this understanding, the **specular values for glass, plastic should be 0.04** while for **water/ice should be 0.02**

However on the UE4 Specular values documentation, the **specular values for glass, plastic is specified as 0.5** while for **water/ice is specified as 0.2**

_ **So I’m confused as to if the UE4 Specular values documentation is incorrect OR am I missing something here ?** _

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**Author:** ![Prouticus](https://d3kjluh73b9h9o.cloudfront.net/original/4X/2/8/5/28502927f1d97ba1051b3b47ccfe17233bf41ef0.png) [@Prouticus](https://forums.unrealengine.com/u/Prouticus)\
**Post date:** [November 29, 2021, 2:02am UTC](https://forums.unrealengine.com/t/correct-value-of-specular-for-pbr-materials/487741/2 "2021-11-29T02:02:23Z")

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Just came across the question as I was researching Ray Tracing in UE4 4.26. This may be too late for you @viduttam but just in case someone else comes along after me…

If I interpret the below ArtStation post (h/t Iri Shinsoj) correctly it sounds like Epic re-normalizes the inputs in UE4 to fit the range that Lagarde describes:

“In Unreal Engine the specular is a value between 0 and 1 and is used to scale the amount of specularity on non-metallic surfaces. It has no effect on metals. In most cases just let the value by default (0.5) which is good for 99% of the materials. Most of the materials reflect 4% of light, when looking strait at the surface. Specular value of 0.5 represents 4% reflection, that said, the specular range 0-1 represents 0-8%. Engine handles the fresnel effect, rising the reflectivity at the angles.”

[https://www.artstation.com/blogs/shinsoj/Q9j6/albedo-chart](https://www.artstation.com/shinsoj/blog)