Fire Protection is Just the Beginning. Designed as a smooth, easy and convenient alternative to conventional firestop packing materials such as mineral wool, fiberglass and backer rod, 3M Fire Barrier Packing Material PM4 is much more than just another non-combustible filler. Its smooth, strong and flexible, and its woven construction is less irritating to the skin when compared to conventional mineral wool commonly used in firestop applications. In addition, it is packaged so users can easily transport...