Abstract: A wall element, of a double walled combustor of a gas turbine engine, comprises an inner, in use, hot surface, and an outer, in use, cooler surface. A plurality of projections is provided on the outer surface to facilitate heat transfer to a coolant flow. The projections are arranged in a first density pattern and in a second higher density pattern for increased cooling. The denser pattern is positioned adjacent a hotter region of the tile than the less dense pattern thereby reducing the thermal gradient throughout the wall element.