A thermal isolation apparatus is provided and includes an annular casing surrounding a turbine bucket stage and defining an annular recess from an interior facing surface thereof, an annular shroud disposed within the casing to provide for a predefined clearance about rotating bucket tips of the turbine bucket stage, the shroud including an annular main member and an annular flange extending from an outwardly facing surface of the main member and being sized to fit within the recess and a thermal barrier formed of porous material, which is interposed between opposing surfaces of the casing and the flange within the recess.