The Surface Properties handle all settings related to the surface of the material, such as the surface roughness and bump. They mainly describe if the surface is polished or rough.
Roughness
Roughness allows you to add tiny imperfections and miniscule details on a surface to make it reflect light in a more diffuse way. The roughness of a surface can range from 0 (perfectly smooth surface) to 100 (pure diffuse). A roughness value of 100 corresponds to a “lambertian” or perfectly diffuse model. It is important to remember that if you want to have very smooth, mirror-like surfaces or clear glass, the roughness should be set to a low value (i.e. 0 to 10).
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It is important to understand how roughness controls the falloff between the 0° and 90° colors, i.e. which of these colors will be most visible. When roughness is low and ND is set to a higher value (Nd 5 or higher), the 90° color will be more visible. As the roughness increases, the 90° color will gradually lose its influence and only the 0° color will be visible. This will happen even with higher Nd values.
Bump Mapping
This parameter, much like the Roughness parameter, allows you to simulate grooves and imperfections on a surface, but at a much larger scale. For example, you can use a Bump / Normal map to simulate wood grain. Keep in mind that Bump / Normal mapping only simulates these grooves on the surface - it does not actually create the geometry in any way, like Displacement does.The "bumpyness" effect depends on the direction and size of the emitter(s) in your scene - a small emitter placed at a low angle to your surface will give a stronger illusion of depth because of the low angle and the sharp shadows that a small emitter creates. On the other hand, a large emitter placed above a flat surface will create a very small illusion of depth.
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Most modeling applications have an option to create a normal map from a detailed model, and there are also applications that allow you to convert a grayscale bump map into a normal map.
Anisotropy
This parameter controls how directional the surface reflections should be. Anisotropic reflections occur on a surface with micro grooves or details that run in one dominant direction. Like an old music LP with grooves that run in an organized circular pattern. These types of surfaces reflect light back in a specular way in the direction of the grooves, and in a more diffuse way in the direction perpendicular to the grooves. Many common materials that have been polished show anisotropic reflections instead of the usual isotropic reflections (that blur equally in all directions when increasing roughness).
You can specify the anisotropy strength (0 for isotropic surfaces – 100 for full anisotropy). You can also set a grayscale texture to control the anisotropy strength: brighter values in the texture specify higher anisotropy. When using a texture, the numeric control has no influence.
Angle
Specify the anisotropy angle; the main direction of the reflected light. You can also set a grayscale texture to control the anisotropy angle. Brighter values in the texture specify a larger angle. When using a texture, the numeric control has no influence.
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