new clear coat paint in unreal 4.4

Does anyone know how to enable this in the material editor (new clear coat) when you create a new material since the release of unreal 4.4 its greyed out and no matter what I try I cant enable it.
I have to missing something

any help will be appreciated
thanks !

You need tho change the lighting model used to clear coat before the input can be used. Is this what you are missing maybe?

You can find the Clear Coat shading model in the left hand side of the Material Editor, in the details tab. With clear coat selected, you will also enable its functions in the material attributes node. =)