Modify
SurfaceFlexibility
The Surface Flexibility command enables you to change the degree and/or continuity of a surface without changing its shape or position in space.
For each of the two parameters (U and V), the values of degree can only be increased (up to 7, in the Deg. U and Deg. V boxes) while the values of continuity can only be decreased (down to 0 in the Internal cont. U and Internal cont. V boxes).
The new surface is more flexible because it is described by a larger number of control points. It is therefore easier to modify it, especially by making local changes to it.
If the selected surface is a specialized one, you are warned that it will be converted into a NURBS and asked whether you want to continue (unless you have deselected the Ask before converting check box).