A fire resistant radiating coaxial cable that employs a high-silica fiberglass yarn spacer is described. The yarn material has mass fraction of silica (SiO.sub.2) between 95.0% and 96.5%, a mass fraction of aluminum oxide (Al.sub.2O.sub.3) greater than 3%, and a mass fraction of calcium oxide (CaO) less than 0.5%. The yarn can be wound in a low-helix-angle helix around the center conductor such that less than half fills the annular space between it and the outer conductor. The cable is configured to maintain a relatively coaxial relation between a center conductor and an outer conductor under intense fire conditions.