A roller table provides a hot material path and heat insulating panels (20) are disposed below that path, between successive rollers (8) of the table. The panels are displaceable between a raised, operative position close to the hot material path and a lower, inoperative position in which the panel upper faces (20') are turned away from said path. The panels remain within the width of the roller table when they are so retracted. Further heat insulating panels (16) are displacably mounted on a frame (14) above the path. Temperature sensing means with the top panels actuate the displacement of both the upper and lower panels.