What is the best PBR real time Fresnel function? I'm working on a physically based renderer, and I've come to a sort of crossroads regarding the Fresnel factor. I'm having trouble finding the best way to represent it. I know that Schlick's Fresnel approximation is based off IOR, but IORs can go up to 38.6 for a meta material, and 4.05 for a natural element, which will make representing these in a 0 1 image difficult and confusing. I also noticed that no one really uses IOR maps. I also read a paper on Unreal's PBR integration, and I discovered that they initially wanted to use a F0 of 0.4, for non metals. What would be the F0 for metals, in this case, and isn't the static value of 0.4 worth the limitations for that tiny bit of memory? I believe the F0 tends to the base color, as it becomes more metallic, but I'd like confirmation. Finally, there's reflectivity or specular, as is used in modern PBR equations. Is there a standard for this, in regard to getting an F0? It seems arbitrary is it a float value up to that directly maps to F0? I am not sure if there are any real reasons to not combine specular color and base color, as Unreal has done this, before. I can't think of a single real reason, even for more stylized implementations. What is the best PBR real time Fresnel function?