220mm Cellcore HX B Under Beam is specially designed to provide foundation protection from ground heave effects when installed beneath reinforced ground beams and pile caps. It is consisted of specially moulded hexagonal cellular Filcor expended polystyrene, available in a number of different depths and grades. Ground movement is caused by the rehydration of clay or expansive shale soils, overburden recovery resulting from deep excavations or, in certain parts of the world, permafrost heave.