Watertightness is an important property for CAD models, yet it is not generally available in commercial systems. This paper introduces watertight hybrid B-spline based B-reps that maintain the original parameterization and representation except in narrow regions around trimming curves, where Bézier triangle type regions seal the model. The new representation matches the model space trimming curve exactly. It can be discretized for analysis and fabrication in a straightforward manner without requiring any post modeling repair operations. We apply this representation to mechanical models and more sculptured models to demonstrate small parametric distortion and arbitrarily small geometric error.