Material graph explaination
By increasing roughness, a surface will become less glossy and more matte. The same amount of light is being reflected from the surface, but adding roughness diffuses that light across the surface. A surface with little or no roughness concentrates the reflected light, giving us sharp reflections and highlights on a surface.
KeyShot allows you to take roughness a step further by using texture maps to define roughness. Black values represent a roughness value of zero (glossy), and white values represent roughness value of 1 (matte). Grayscale values will be respected, such as 50% gray resulting in .5 roughness. Using roughness textures in KeyShot can save you from separating surfaces that will have more of a glossy or matte finish on your products. To increase realism, roughness textures can be applied to add minor surface defects or grime such as skin oils, light abrasions or even dust.
In the CG (computer graphics) world, a bump texture is a grayscale image that simulates peaks and valleys on the surface of geometry. The peaks catch light and cast shadows while the valleys recede and reflect very little light. The result of using bump textures is an appearance that the detail was modeled into the geometry. Rather than modeling a highly intricate texture such as leather or wood grain, we rely on texture maps in KeyShot to add realism to our renderings without having to painstakingly model every intricate detail.