http://cagd.cs.byu.edu/~tspline/index.html

T-splines are a revolutionary patent-pending surface type. NURBS and subdivision surfaces are both special cases of T-splines. Thus, T-splines inherit all of the respective strengths of NURBS and subdvision surfaces (SubDs) while eliminating most of their weaknesses.

A T-spline can be thought of as a NURBS surface for which a row of control points is allowed to terminate, without traversing the entire surface.This simple idea imbues T-splines with several significant advantages over NURBS, such as the ability to eliminate superfluous control points, to perform true local refinement, to merge two NURBS surfaces, and to add local features

A T-spline can be thought of as a NURBS surface for which a row of control points is allowed to terminate, without traversing the entire surface. This figure (left) shows a T-spline control grid (or T-mesh) next to a NURBS control grid. This simple idea imbues T-splines with several significant advantages over NURBS, such as the ability to eliminate superfluous control points, to perform true local refinement, to merge two NURBS surfaces, and to add local features.

Cubic NURBS and SUBDs can be converted to T-splines (or T-SubDs) without any error. Likewise, T-splines can be converted into cubic NURBS without error. This means that T-splines integrate effortlessly into modeling environments that involve special-purpose NURBS or SUBD programs.