PBR 3D model stretching when applied usually comes from distorted UV mapping (misaligned texture coordinates) or texture scaling that doesn’t match the UV layout.
UVs act as a "map" for PBR textures (like albedo or normal maps) to wrap around the model—if they’re stretched, squashed, or poorly unwrapped, textures can’t align correctly, causing distortion. Using a texture with a resolution or scale incompatible with the UVs (e.g., a small texture on a large UV area) also leads to stretching.
To fix this, re-unwrap the model’s UVs for uniformity and no overlaps, or adjust the texture’s scale in your 3D software to match the UV layout without distortion.