Anisotropic reflection
A reflection stretched along the grain of a surface, like the long highlights on brushed metal, satin, and hair.
See it
What it is
An anisotropic reflection stretches differently along one surface direction than across it. Tiny aligned grooves in brushed metal smear a highlight into a streak; hair fibers stretch it along the strands. An isotropic rough surface has no preferred direction, so its highlight spreads evenly instead.
Reach for anisotropy on brushed aluminum, stainless cookware, satin, vinyl records, and hair. The direction matters as much as the strength: straight brushing needs a consistent tangent, while a machined disc needs the direction to turn around its center. glTF carries the settings through the KHR_materials_anisotropy extension.
Gotcha: anisotropy exposes bad UVs and tangent data immediately. A seam or rotated UV island makes the highlight snap direction. It also needs something useful to reflect, so test it under a studio environment map with long, readable light shapes rather than an empty scene.
Ask AI for it
Make this brushed aluminum in three.js with MeshPhysicalMaterial: set metalness to 1.0, roughness near 0.35, anisotropy near 0.8, and align anisotropyRotation with the visible brushing direction. Supply an anisotropyMap when the grain direction changes across the surface, keep the mesh tangents and UV islands aligned, and light it with a studio HDR environment map containing long softboxes.