Roughness and metallic maps, explained
Roughness and metallic are the two maps that do the most to define what a PBR surface feels like — plastic or polished, rusted iron or painted steel. They're separate channels with separate jobs, and they work together.
The short answer
The roughness map controls how blurry or sharp a surface's reflections are: black (0) is a mirror, white (1) is fully matte. The metallic map is almost binary — white (1) means metal, black (0) means non-metal. Most of a material's character comes from varying roughness; metallic stays mostly 0 or 1, with in-between values reserved for transitions like partly-rusted metal.
What roughness does
Roughness describes microsurface detail too small to model — the micro-scratches that scatter reflected light. Low roughness gives tight, sharp reflections (polished metal, glossy paint); high roughness gives soft, spread-out reflections (chalk, raw wood).
It's the single most expressive PBR channel. Varying it across a surface — fingerprints, water spots, worn patches — is what sells realism, far more than the base color alone.
What metallic does
The metallic map tells the renderer whether to treat a pixel as a metal (conductor) or a non-metal (dielectric). Metals reflect their base color and have almost no diffuse component; non-metals reflect white-ish highlights and show their diffuse color.
Keep it mostly pure black or pure white. Gray metallic values are physically rare and usually a mistake — the main exception is material boundaries, like chipped paint revealing steel underneath.
How they work together
A surface reads as “rusted iron” because metallic marks the bare-metal areas while roughness makes the rust dull and the clean metal sharp. The two maps are usually masked from the same wear pattern.
Authoring roughness and metallic in tandem — not in isolation — is the core of believable PBR texturing.
Frequently asked questions
What does the roughness map control?
How sharp or blurry reflections are. Black is glossy and mirror-like, white is matte. It's the most expressive channel for conveying how a surface feels.
Should the metallic map use gray values?
Rarely. Metallic should be almost pure black (non-metal) or pure white (metal). Gray only appears at transitions, like rust or chipped paint.
Is roughness the same as Unity's smoothness?
They're inverses. Unity uses smoothness = 1 minus roughness, so a rough surface has low smoothness. Many tools (including Mixos) export roughness; invert it for Unity.
Dial in roughness and metallic with live 3D feedback in Mixos — see reflections change as you paint.