Hi Pilou - also just to clarify, it is not unusual for Sub-d tools to only deal with polygon mesh data.

That is, they often will take in a polygon mesh structure as the "hull" of the sub-d surface, and then it is not unusual for the output after subdivision to also be polygons as well.

That is probably the case with the tool that you are mentioning, even if it has an internal mechanism where it works as NURBS.

To get a NURBS export, it needs to export surfaces to a NURBS file format like IGES or 3DM.

- Michael