Which moves easily through fiberglass insulation. It helped but sadly, the air still moved through. But the housewrap will hold rain water that comes in through plastic window sash channels, poor trim design joints and siding leaks. It only takes a few years to rot OSB sheathing. Only a few more to rot plywood.

I work hard to form air barrier envelopes, inside and outside, when I build or restore old homes. The more barriers, the better, especially when working with fiberglass insulation. One of the most effective I've found is to design the drywall installation so the bottom sheets lay on the sublfoor. Those are caulked to the subfloor seam. Once the rest of the drywall is installed and taped, you have a very effective air infiltration barrier envelope.

Today though, the spray foam is the best way to go. Expensive, but as well as better insulation performance, it is also an air barrier.