To paint a roughness 3D model, import the model into texturing software (e.g., Substance Painter, Blender) and use a roughness brush to apply grayscale values—light gray for rough surfaces (which scatter light) and dark gray for smooth ones (which reflect light).
Roughness painting defines how a material interacts with light, so use layers or masks to target specific areas: for example, make a metal screw smoother (dark gray) while adding rough wear to its plastic handle (light gray).
If you’re new, start with a neutral base roughness (e.g., 0.5 for matte materials) and build subtle variations with a soft brush—this avoids overdone details and keeps the material realistic.