refraction and therefore there is relatively little visual interference with the pattern details 25 of the wall 12 this preservation of wall patterns is particularly beneficial in the case of finely patterned wallpaper at the extreme periphery of the bumper 21 there may be provided a relatively more strongly curved 34 break 34 24 a relatively abrupt truncation of the shallow curvature of the surface 23 this change of curvature serves to provide greater strength and uniformity of appearance than would be obtained with a relatively sharp peripheral 34 edge 34 as previously mentioned the convexity of the overall frontal surface 23 of the bumper 21 helps to hide the periphery of the bumper it brings the periphery whether a curved break or a sharp edge very close to the underlying wall surface placing the periphery so close to the wall minimizes the possibility of refractive displacements of the underlying pattern as well as the possibility of noticeable shadows cast by the bulk of the bumper onto the wall in short if the break is sufficiently close to the edge and therefore very close to the underlying wall surface when the bumper is installed refractive and umbral effects will be unnoticeable in normal use to help keep the refractive effects small even when the break is positioned at the extreme periphery of the bumper 21 the 34 break 34 24 is preferably given some curvature rather than being made a sharply defined edge the invention is not limited to generally circular bumpers 21 such as that shown in fig3 but may also.