The new Solidify deformer lets you create areas of geometry that appear more solid on deformed geometry, which lets you define rigid parts of a character's clothes, such as buttons or a belt buckle.
The Solidify deformer works by analyzing deformed sections of geometry and dividing it into separate polygon islands. Each polygon island is then replaced by the original geometry moved and blended into place based on the approximation of the matrix derived from the deformed vertices.