Abstract: In a cooling surface cladding for polygonal chambers of steam generators with a hopper-shaped floor and fired on the circulating fluidised bed principle, which consists partially of substantially vertical finned tubes extending in the manner of walls between manifolds and converging curves in the floor region to form a hopper, two opposite finned tube walls (1) in the hopper region, viewed from top to bottom, first form a hopper wall (1') inclined from the vertical over their entire width and then form at least one vertical hopper wall (1") of decreasing width and with partially oblique manifolds (2). In the region of the hopper, viewed from top to bottom, the adjacent tube wall (3) and the tube wall (3') opposite it form first a vertical hopper wall of diminishing width and with oblique manifolds (4) and then an inclined side wall (3") of the hopper of constantly reducing width.