Over the years, many studies have shown the deleterious effects of dielectrics in cable construction. The type of dielectric material is very important. A perfect vacuum is the best dielectric followed by air and fluorocarbon plastics such as Teflon and its variants, PFA and MFA.
Basically, too much plastic insulation in a cable can lead to sonic coloration and veiling of the signal. Since magnetic fields surround the entire cable, the cable sheath adds to this sonic signature. Our goal with our cable designs was to minimize dielectrics and in our case, the only dielectrics employed are the MFA cores and the wire air-cores.