The spec can be found in either
https://benhouston3d.com/blog/extended-wavefront-obj-mtl-for-pbr/
or Internet Archive: https://web.archive.org/web/20230210121526/http://exocortex.com/blog/extending_wavefront_mtl_to_support_pbr
- Kd/map_Kd (base/diffuse) // reuse
- Ks/map_Ks (specular) // reuse
- d or Tr (opacity) // reuse
- map_d/map_Tr (opacitymap) // reuse
- Tf (translucency) // reuse
- bump/-bm (bump map) // reuse
- disp (displacement map) // reuse
PBR material parameters as defined by the Disney PBR.
- Pr/map_Pr (roughness) // new
- Pm/map_Pm (metallic) // new
- Ps/map_Ps (sheen) // new
- Pc (clearcoat thickness) // new
- Pcr (clearcoat roughness) // new
- Ke/map_Ke (emissive) // new
- aniso (anisotropy) // new
- anisor (anisotropy rotation) // new
- norm (normal map) // new
EoL.