An insert for a radiant tube of a furnace including a first section adapted to absorb heat from combustion gases passing through the radiant tube and radiantly transfer the heat to a wall of the radiant tube and a second section for directing heat and gases in the radiant tube toward the first section of the insert and a system including a radiant tube and one or more such inserts. Also, a method of improving heat transfer from a radiant tube of a furnace to the material being heated including supplying an insert as described above and placing the insert into the radiant tube such that the first section corresponds to a portion of the radiant tube that is closest to the material being heated. Also, an insert for a radiant tube of a furnace including a ceramic body and a metal deposited on the surface of the ceramic body.