PBR texture maps explained

Physically based rendering, or PBR, is the material system used by nearly every modern engine and 3D tool. Instead of one painted image, a PBR material is a set of textures, each describing one physical property of the surface. The renderer combines them with the scene’s lighting.

That separation is the whole point. A painted texture with a highlight on the left looks wrong as soon as the light moves to the right. A PBR material describes the surface, not a picture of it, so it looks correct in any lighting.

Maps are painted onto the model through its UV layout; if that part is new to you, start with UV unwrapping explained. This guide covers the metallic-roughness workflow, which is what glTF, Unity, Unreal Engine, Godot and Blender use by default.

Base colour (albedo)

The colour of the surface with no lighting at all: no shadows, no highlights, no reflections. For non-metals it is the paint colour. For metals it is the colour of the reflections, which is why gold has a yellow base colour and steel a light grey.

How to spot a problem: visible shadows or bright spots in the base colour. They will fight with the real lighting. This is the most common flaw in AI-generated textures, usually inherited from a reference photo with hard light.

Roughness

A greyscale map describing how smooth the surface is at a microscopic level. Black (0) is mirror-smooth with sharp reflections. White (1) is rough, like chalk or concrete, scattering light so reflections disappear.

Roughness often carries more visual information than colour. Fingerprints on glossy plastic, worn paths on a wooden floor, and polished edges on metal are all roughness variation. In the texturing demo you can drag the roughness slider and watch reflections go from crisp to soft.

Note: some tools use a glossiness or smoothness map instead, which is simply roughness inverted.

Metallic

A mask saying whether each part of the surface is metal (white, 1) or not (black, 0). Real materials are almost always one or the other, so this map is usually close to pure black and white. Grey values are useful mainly at transitions, for example where paint is chipped and bare metal shows through, or for dust on metal.

How to spot a problem: large areas of mid-grey on materials that should clearly be metal or not, which makes them look like plastic pretending to be metal.

Normal map

A normal map fakes small surface detail. Each pixel stores a direction, encoded as RGB, that tells the renderer which way the surface is facing at that point. Light then responds as if there were bumps, grooves or scratches, even though the geometry is flat.

This is how a low-polygon model can look detailed. When you remesh a dense model to a low triangle count, the lost detail is baked into a normal map so it still reads correctly.

How to spot a problem: lighting that looks inverted (bumps that look like dents). That usually means the map was made for the other convention: OpenGL-style (Y+, used by glTF, Blender, Unity) versus DirectX-style (Y−, used by Unreal Engine). Flipping the green channel fixes it.

Ambient occlusion (AO)

A greyscale map darkening creases and contact points where ambient light would struggle to reach. It adds depth, especially in engines without real-time global illumination. It is optional; some engines compute it at runtime instead.

Emissive

Areas that glow on their own: screens, LEDs, lava, the glass of a lamp. Emissive does not usually light other objects unless your engine has global illumination, but it stays bright in a dark scene. The boombox sample uses emissive for its display.

Packed textures

To save memory, engines often pack several greyscale maps into the channels of one image. glTF packs roughness into the green channel and metallic into the blue channel of one texture. Unreal Engine commonly uses an “ORM” texture: occlusion in red, roughness in green, metallic in blue. threeD can export either layout.

Summary