Far and away the more commonly used of the two. Provides all of the above benefits at a much more affordable price.
The interior wall or “Inner Leaf” is sheathed, flashed, and covered with an air vapor barrier.
Air is allowed into the cavity behind the “Outer Leaf” to provide some pressure equalization keeping much of the rain water out of the cavity. Some small amount of rain water is expected to get behind the cavity and this moisture is both drained from the system and also dried by the flow of air in the cavity.