During dyno testing, with an engine under load and with only 1/2'' air gap clearance, exhaust manifold temperatures reached 1000F. Meanwhile, the Accel Extreme 9000 Heat Reflective protected boot's internal temperature never exceeded 430F--even after 2 hours of continuous abuse! The Extreme 9000 Heat Reflective technology is not a paint. It is a multi-step process using patented materials. Permanently bonded to the Accel spark plug boot, it will not rub, peel or flake off and stays as flexible as the silicone spark plug boot itself. The heavy duty stainless steel alloy winding, aramid/fiberglass core and stainless steel spark plug terminals make these some of the best firing, longest lasting wires you'll own!