It is an open problem that the net of any convex polyhedron can be unfolded onto a flat plane with no overlapping. Is anything known if we allow x faces to overlap? For example, is it known if any convex polyhedron can be unfolded with a maximum of 2 faces overlapping? What about the more general case of a polyhedron that is topologically convex (that is, its graph is isomorphic to the graph of a convex polyhedron)?
This paper provides an example of an open polyhedron without a net that is topologically convex, and the closed case appears to be taken care of by this paper (mentioned in an answer below). One solution to the topologically convex case would then to be to find a procedure to modify either polygon so that the number of overlapping sides increases without bound. I have been unable to do so without breaking the topologically convex property, but it seems a reasonable task.