i think backing plate. bec there is nothing in the hub assembly that needs heat protection. in the first place, it is subjected to continuous heat while running.... it happened to my car before. i had the ball bearing replaced and the mechanic bent the plate towards the rotor disc. so it grinded the rotor and damaged it. still is usable pero meron lubog on the inner side of the rotor disc. maliit lang ang clearance nito. slight bent or misalignment in installation, it will already touch the disc.