In Maya you can convert basically all structures, even Fluids, into Polygon meshes. NURBS surfaces on the other hand cannot be converted directly into Polygons. They need to be constructed by hand from the Poly meshes.
Since “construction” is at the heart of CGI modeling, I demonstrate two methods to turn a Polygon surface into a NURBS surface. The result is by definition never identical with the original. But in many cases the result, since it’s an elegant NURBS surface, is very versatile for modeling needs such as building homogenious paths between surfaces as in this tutorial: