Skinning binds a mesh to a set of joints so that moving the joints deforms the surface.
How a surface follows a skeleton
Each affected vertex has weights describing how strongly particular joints influence it. Near an elbow, vertices may be influenced by both the upper arm and forearm. As the joints move, those influences combine to determine the new surface position. The weights are part of the deformation setup; they are not a painted colour texture.
Bad weights show up in motion
A model can look excellent in its resting pose and collapse when it bends. Unexpected pinching, stretching or a distant patch moving with the wrong joint often points to weighting or bind-pose problems. More polygons alone will not repair incorrect influences. The topology and range of poses need to work with the weighting.
What to check before publication
For an animated character in Painta, examine elbows, shoulders and other tight bends in the exported GLB, not just in a still preview. Try the most extreme pose in each clip. The accompanying animation uses a simple flexible strip to show how a surface follows two connected segments. It illustrates the principle; a production character usually needs more careful geometry and weights.
Related concepts and further reading
Khronos: skins and joint weights
Continue with Joint (3D Animation) for a closer look at this part of the experience.