A method of continuously roll-forming substantially flat strip material, to form an elongate product (1) having a non-planar profile, by imparting a curved or angled profile to each of a plurality of longitudinally extending fold zones (3) of the strip, and straining each of a plurality of longitudinally extending protective zones (5) so as to elongate each protective zone (5) and thereby alleviate defects in the product due to longitudinal contraction of the fold zones (3), characterised in that at least one edge of each protective zone (5) is out of register with either edge of an associated fold zone (3).