That region of the tube surrounding the line of tangency which is in a plastic state during the bending process. Therefore, the point of bend is not synonymous with line of tangency. The point of bend refers to a part of the tube, whereas the line of tangency defines a fixed plane in space through which the tube passes as it is bent. It is important to understand the point of bend as region rather than a geometrical element, because good bend quality requires fixturing the mandrel and the wiper die properly to control the flow of material in that plasticized region. For example, the reason why the mandrel nose must be set past the line of tangency and into the arc of the bend is because the point of bend exists both behind and ahead of the line of tangency and needs to be supported by the mandrel nose to prevent it from buckling or collapsing in its plastic state.