The fiberglass core is covered by a layer of ferrite magnetic material wrapped with variable-pitched metal wire. This produces the impedance necessary to supppress radio frequency interference throughout the entire spectrum thus suppressing ignition noise on AM, FM, CB and mobile radios. The outer jacket insulation features either NGK's more highly heat resistant EPDM rubber compound, "see-thru" polyvinyl chloride, or NGK's new silicone insulation, dependent on which is the best for each individual application
