Types of Layers: Specular Layer
In the same way that a diffuse layer incorporates its own diffuse grain, a specular layer incorporates its own specular grain. This approach provides better hierarchy of the layer parameters and provides more options. The specular layer is parameterized in the same way as the parameters under the reflection tab for the standard material.
A specular layer operates in additive mode: the reflection is added to the combination of lower layers, but provides overall filtering of the lower layers and variable attenuation according to the Fresnel reflection. If the Transmission attenuation option is ticked, then some of the reflected light on the surface is not transmitted to the lower layers, making the light behave realistically.
You will find in the accordion menu Roughness the Roughness map parameter and Gloss map only after enabling the roughness and then dragging and dropping a texture from the texture library on the None field.
The Roughness map is a grayscale texture where the black corresponds to a roughness of 0 (smooth) and white corresponds to a roughness value of the material.
On the other hand, the Gloss map is a grayscale texture where the black corresponds to ta value of the material roughness and the white corresponds to a roughness of 0 (smooth).
You will find in the accordion menu named Mapping the following parameters Allow repeat in U and Allow repeat in V that allow you to choose to repeat the texture in U and/or V.
By checking the Mirrored checkbox you can reflect the texture in U and/or V.