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Cook-Torrance has a different look. At higher glossiness settings, the highlight becomes a hard-edged disc, which is good for glassy, or more mirror-like polished surfaces. This is great for car finishes, glass, water, chrome, or anything else you would expect to see your reflection in. At lower glossiness settings, the shader gives really nice highlights for other materials, like unpolished metal, or frosted glass. It creates a very wide diffused highlight, which can be really useful for less reflective surfaces like wood, stone, skin, or other surfaces that don't have much of a reflective quality.