# When to use fresnel

Hi, I’ve been wondering about when to use a fresnel node to mix between a diffuse and glossy shader and - correct me if I’m wrong - my conclusion is that all materials do have an IOR value but that it’s not worth using when it’s greater than 2, since it’s very smooth at those values.

Heh, long sentence - short question :yes:. Pls correct me if I’m right in my thinking.

Thanks!

I use “some kind of fresnel” for everything. The normal fresnel I use only when I’m forced to, like for refractive/gloss materials. Otherwise I I will use a facing^5 which is then rescaled to 0.04-1, similar to PBR approaches. For metals, I use facing as is, but plug in facing and edge colors similar to this paper and will eyeball it or find other references if I don’t have the colors available (example only have a couple of metals in it).

That said, I don’t use glossy for everything like some people suggests. If material is very rough and (by testing) it doesn’t produce too much of a difference if disabling it, I will happily disable it to obtain better render times. Or mix in velvet shader instead where appropriate, to make it appear to “interact with light”.

I use fresnel to make glossy plastics and ceramics. The default value seems to work quite well.

You are correct that the fresnel effect is lost at values much above 2.

Hi,

Well technically IOR is ‘index of refraction’ and is important for when light passes through an object, like the glass shader.
The Fresnal node effectively gives a factor value depending on the IOR and the angle of incidence of the ray
When people use it for mixing glossy and diffuse they are using the factor to mix the shaders depending on the ray angle
And in this case high values of IOR would cause a higher factor from the Fresnal node which do have an effect >2 !

Here is an illustration:

Here {if you look at the node setup} the IOR comes from the X coordinate so each object has an IOR ranging from 0 to 10
You get weird {but useful!} effects with an IOR from 0 to 1 where the Fresnal node is generates a factor of 0 or 1 depending on the angle.
{The smaller spheres have an IOR from 0 to 1}
With an IOR >1 you can see the lower diffuse node being mixed in, more at low angles of incidence

Hope this helps

Martin

Thanks, I think I get fresnel now.
But when should I use “facing” instead fresnel?

Thank you all!