Roughness Map
Surface microfacet detail
Definition
A roughness map is a grayscale texture controlling how rough or smooth each pixel of a surface appears to light. Black (0) is mirror-smooth (sharp reflections), white (1) is matte (diffuse, blurred reflections). It is arguably the most important PBR channel for selling material identity — wood, metal, wet vs dry surfaces, finish quality.
In production
Production roughness maps almost always vary across a surface: edges are more polished from wear, recessed areas are dusty and rougher, fingerprints darken metal. Substance Painter generates plausible roughness automatically from curvature and AO maps as a starting point, then artists refine it with hand-painted masks or procedural generators like "Dirt" and "Edge Wear." Marmoset Toolbag and Unreal Engine 5's material editor both preview roughness under high-frequency IBL lighting, which is the fastest way to catch banding or flat, unvarying roughness that reads as "plastic." A common mistake is treating roughness as a single global value per material — a rusted iron railing needs roughness ranging from about 0.3 (worn metal high points) to 0.9 (flaking oxide) across a handful of centimeters. Roughness also interacts with the specular channel and IOR: at grazing angles even a rough dielectric surface shows a bright Fresnel rim, so it can't be tuned in isolation from viewing angle when validating a material in Marmoset's turntable view.
