PBR Materials Explained: Base Colour, Roughness, Metallic and Normal Maps

Physically based rendering, usually called PBR, is an approach to materials and lighting that models how light actually interacts with surfaces. Its big advantage is consistency: a correctly built PBR material looks right in daylight, under studio lights or at night, because it describes the surface rather than faking a particular lighting setup. Most modern renderers and game engines use it.

The core texture maps (metal-roughness workflow)

Base colour (albedo)

The surface's colour without any lighting or shadow information. A common mistake is using photographs with baked-in shadows and highlights; those will double up with the renderer's own lighting. Base colour maps for most non-metals should avoid pure black and pure white.

Roughness

A greyscale map controlling how smooth or rough the surface is at a microscopic level. Black (low roughness) produces sharp, mirror-like reflections; white (high roughness) produces broad, soft highlights. Roughness variation, such as fingerprints, wear and smudges, is what makes surfaces look real.

Metallic

Tells the renderer whether a surface is metal. In practice it is usually close to black or white: raw metals are white, everything else, including painted metal, is black. Values in between are mainly for transitions such as worn paint revealing metal.

Normal map

An RGB image that fakes small surface detail, such as grain, stitching or bumps, by changing how light hits each pixel without adding geometry. Normal maps come in two conventions (often called OpenGL and DirectX) that differ in the green channel. If bumps look inverted, flip the green channel.

Ambient occlusion (AO)

A greyscale map of small crevices where ambient light is blocked. Many path-traced renderers calculate occlusion themselves, so an AO map may be unnecessary or should be used subtly.

Height or displacement

A greyscale map used to physically displace geometry or create parallax effects. Displacement adds real depth to surfaces such as stone walls or paving, at a cost in render time and memory.

Colour space: the setting that breaks materials

This is one of the most common causes of "something looks off". Only colour maps should be interpreted as colour (sRGB). Data maps should be read as linear or "non-colour":

• sRGB / colour: base colour
• Linear / non-colour: roughness, metallic, normal, AO, height

A roughness map loaded as sRGB will appear rougher or shinier than intended, and a normal map loaded as sRGB will shade incorrectly.

Metal-roughness vs specular-glossiness

There are two main PBR workflows. Metal-roughness uses base colour, metallic and roughness maps and is the most widespread. Specular-glossiness uses diffuse, specular colour and glossiness maps; glossiness is roughly the inverse of roughness. Material libraries usually state which workflow they use; converting between them needs care.

Scale matters

A wood grain or brick texture applied at the wrong scale instantly reveals a render as artificial. Model in real-world units, use textures with known physical dimensions, and check scale against a reference object such as a door, which is roughly two metres tall.

Common mistakes

• Perfectly uniform roughness: real surfaces are never this clean
• Painted surfaces set as metal
• Shadows and highlights baked into base colour photos
• Obvious repetition of tiled textures across large areas; break it up with variation maps or decals
• Wrong colour space on data maps

Where to get good materials

Free CC0 libraries such as Poly Haven provide scanned and procedural PBR materials with all maps included and real-world scale information. Studying how a high-quality library material is built is one of the best ways to learn. For the lighting side of the equation, see our interior rendering lighting guide.