I have recently used 4" thick rock wool to insulate a room of a cape cod (exterior walls) for the first time. When we went to buy the insulation, Depot had a huge display of it for sale. In my area, it has not really been for sale recently. I have seen it being used all of the time on TV but that is in very cold climates. I felt that it was alot easier to install and cut to fit odd size openings and want to use it again if available. I had sprayed the walls first with an inch of closed cell because i had done the roof with the spray as well. So after all of my research that seems to sometimes confuse me, do i NOT need the paper face of fiberglass in order to have the correct vapor retarder if i use spray foam first? What is the differance of rock wool compared to fiberglass?? I once had to put it on a wall for a commercial oven before i installed some sheet metal for a hood fan to make code, so i know it will not burn but why all of a sudden is this product readily available??