The best way to paint a PBR 3D model is to use PBR-focused tools (like Substance Painter or Blender’s Texture Paint) to create layered PBR maps (albedo, metallic, roughness, normal) and use real-time previews to ensure material accuracy.
PBR maps simulate real-world traits: Albedo sets base color (e.g., blue for a mug), metallic controls reflectivity (shiny steel vs. matte rubber), roughness defines smoothness (glossy vs. worn), and normal maps add subtle depth (scratches, grooves). Sync textures with your model’s UVs to avoid stretching.
For beginners, start with simple materials (like a plastic bottle) to practice balancing metallic/roughness values—many tools have preset PBR materials to learn workflows without starting from scratch.