A composite thermal insulation panel for a metal processing installation has a thin-walled casing providing a cover plate or membrane that will be heated quickly to near the temperature of an adjacent hot metal slab or strip being processed. To allow substantial freedom for movement relative to adjoining regions of the casing due to thermal expansion caused by the large temperature changes, retaining elements of the casing that locate the membrane transversely to its extent but permit relative movement in its own plane, and/or the membrane may have surfaces that slope to a central region to accommodate relative thermal expansion by flexure. Panels below the material path may have membrane surfaces that slope downwards to an escape aperture for scale dropping from the hot metal. Panels above the material path may have apertures aligning with the lower panel apertures for temperature sensors that detect the passage of hot material between the panels. Control means may be provided to displace the panels in response to the sensed transverse temperature profile to maintain the profile more uniform.