Cartons are a common means for packaging a variety of items. These are usually “erected” by dedicated machines which fold the carton into shape from a flat net. When there is a need to use new forms of cartons, dedicated machinery may not be appropriate and reconfigurable systems may be used instead. There is a need to simulate the erection process itself to ensure that this behaves as expected. This paper investigates the use of constraint-based techniques to produce such a simulation. The necessary commands are generated from the geometry of the carton net. Geometric constraints are imposed to ensure that the net remains intact and so resolve cases where loops of faces are present.