ACCEL 4044 SuperStock 8mm 4000 Series Yellow Graphite Spark Plug Wire Set Fiberglass and Kevlar stranded inner core 8mm yellow silicone jacket with fiberglass braid High density, high durometer with Ethylene Propylene Diene Monomer insulation Silicone jacket with fiberglass braid is rated at 450 degrees Fahrenheit Conductive high resistance carbon graphite suppression material