A sheet of cold rolled material having on both of its surfaces rows of projections and rows of depressions, the projections on one surface corresponding with the depressions on the other surface, the relative positions of the projections and depressions being such that lines drawn on a surface of the sheet between adjacent rows of projections are non-rectilinear, the sheet having a base gauge G, wherein each projection has a substantially continuous region of peak plastic strain at, toward or about its apex and/or is thinned by no more than 25% of its base gauge G. Methods of forming the sheet material and tools for forming the sheet material are disclosed.