At risk of hijacking the thread, it depends on the layering system the manufacturer uses to construct the garment. This info comes from a rep of a leading manufacturer of waders.
The single layer system bonds the breathable membrane to the inside of the fabric shell of the garment (nylon, etc.). Therefore the membrane is subject to abrasion from the inside as you wear the garment.
The two layer system is the same but adds a interior liner layer to guard against abrasion.
I think he also said there is a three layer system with the outer fabric layer, the membrane as a separate layer not bonded to the outer layer, and the liner layer.