Non-toxic and organically bound, IGS Industries' Mill-Pac Black expands to form a tight seal in your fireplace or stove that will provide years of reliable service. Mill-Pac Black will not shrink or crack, and is inert to combustion byproducts. Several major wood, pellet, and gas stove appliance manufacturers specify Mill-Pac Black as their sealant of choice! Mill-Pac Black is formulated using Non-RCF refractory fibers, which eliminates OSHA and EPA concerns with the use of these raw materials. Mill-Pac Black is still rated to a 1050°F (565oC) max continuous operating temperature, and has excellent resistance to erosion by gas or wood combustion byproducts. Since Mill-Pac Black has always been formulated with an organic, non-toxic binding system, it has been considered a green product. With the elimination of RCF fibers, Mill-PAC Black is truly environmentally friendly.