When mixing opacity for 3D models in a PBR workflow, use an opacity map (or alpha channel in texture maps) to control per-pixel transparency and integrate it with core PBR properties like base color and roughness.
The opacity map uses grayscale values: 0–50% makes areas more translucent (e.g., thin fabric, glass), while 50–100% keeps them opaque. For smooth transitions (like foliage or frosted plastic), enable alpha blending in your renderer and align the opacity map with other PBR maps—use base color for tinted glass or roughness for matte transparency—to maintain physical realism.
For testing, try a simple object (e.g., a transparent leaf) in Blender or Substance Painter. Gradually adjust the opacity map’s grayscale values to balance transparency with the PBR material’s authenticity.