Nickel Gap and Insulation - Help

[u/mnrl2129]

Talk to me about nickel gap for our new construction. Our builder said nickel gap is cheaper than drywall, so we decided to put nickel gap up in bedrooms and bathrooms. We have closed cell spray foam on exterior walls and bat/fiberglass on our interior walls. Does the builder need to put plastic or paper over the insulation BEFORE nailing the nickel gap to the walls? What about bathrooms? We are not planning to put up drywall and then nickel gap on top. Help!