When using opacity on 3D models in Substance Painter, seams typically come from misaligned UVs or inconsistent alpha blending across UV edges.
- **UV seams**: Where model faces are split for texturing, these break the continuity of opacity textures, leading to visible mismatches at edges. - **Alpha blending issues**: Inconsistent alpha sampling in the material shader can exaggerate these gaps, making seams more noticeable.
To fix this, move UV seams to less visible areas, increase texture padding during baking, or adjust the material’s alpha blending settings in Substance Painter.