You can copy-paste this code to the Python console to extract the surface and put it into a new mode node.
volMesh=getNode('Model').GetMesh()
extractSurface=vtk.vtkGeometryFilter()
extractSurface.SetInputData(volMesh)
extractSurface.Update()
slicer.modules.models.logic().AddModel(extractSurface.GetOutput())
You can extract a specific material by adding vtkThreshold filter before vtkGeometryFilter.