The hard material polytetrafluoroethylene (PTFE) is an insulating material for cables, which is used as dielectric and the cable sheath and has the DIN/VDE designation 5Y. It is also known under DuPont's trademark Teflon.
It is arguably the most chemically and thermally resilient polymer and is characterized by a very low dielectric constant of 2.2 and a low loss factor of 1.5, at a microwave frequency of 3 GHz. PTFE can be used in the temperature range from -190 °C to +260 °C and has a melting point of 342 °C. It is characterized by high thermal stability, is non-flammable (n.e.f.), has low water absorption and is largely resistant to chemical attack.
PTFE dielectric is also available with air chambers. This is called expanded polytetrafluoroethylene (ePTFE). Due to the air-PTFE combination, ePTFE has a permittivity of 1.3 and an extremely low miss angle at frequencies in the gigahertz range.