Location: Minneapolis/St. Paul, Minnesota - Latitude 45.057 Longitude -93.074
attic vapor barrier
Yes. In your climate a vapor barrier should be on the warm side of the insulation as a simple answer.
A definition of a vapor barrier is not absolute, but is just a number selected to separate materials between being "vapor barriers" and not being " vapor barriers". all it takes is 1/2 mil of thickness to throw poly into a differen category even though they have a range from .5 to 6. Other materials can be much better. - On top of this is the installation that is even more importanr in the real world. Multiple layers may be used if the difference is below a specified limit, but few people are able to handle the calculation and design.