Plenum rated wire with solid bare coper conductors, color coded.  300 volt rating. FPLP power-limited fire alarm plenum cable is listed by the NEC as being suitable for use in ducts, plenums and other space used for environmental air.  All FPLP cables are listed as having adequate fire-resistant and low smoke-producing characterizes must pass both UL test 1424 and UL tunnel test 910.