Materials change the model’s surface “feel”, meaning that they provide the illusion of various external properties for models, such as roughness, transparency, reflectivity, and shine.

These external properties simulate the model’s substance and determine how we perceive an object.

A. Material used for color B. Material used for color and detail

In the image above, two copies of the same bottle model are shown. The first bottle has a material applied simply to provide color, and the second bottle material has had the Bump Map settings changed to simulate detail, as well as color.

Note how changing the settings changes the appearance of the bottle from a smooth ceramic or plastic to a shinier, dirty glass. The geometry of the model has not been changed, only the material, shaders, and textures applied to it.