  Quenching of thermal emission above 0 K is an unusual material property,
essential for future energy, transportation, and space technologies. Despite
the great effort invested, nearly complete quenching of thermal radiation
rather than some reduction of its flux has only been achieved at low
temperatures (below 373 K) and in narrow spectral windows using complex
techniques suitable only for small scale objects. In this work, we present a
light and flexible composite material that can suppress propagating photonic
modes and, in this way, quench thermal radiation while preserving heat transfer
(by thermal conduction) at a room and higher temperature below 600 K. This has
been achieved by altering the local photonic density of states and
consequentially the thermal properties of carbon nanotubes forming a
percolating nanofiber network with a thermostable polymeric matrix.
