Abstract: A method for imparting resistance to axial displacement of convolutions in a convoluted substrate of the type comprising spirally wound superimposed plain and corrugated strips of metal which are suitable for use in supporting a catalyst in a catalyst unit in which the substrate is washcoated with a layer of refractory metal oxide and is useful for the purification of exhaust gases, especially exhaust gases from a motor vehicle. The method comprises making one or more weld runs across an end face of the substrate so as to weld together the plain and corrugated strips at points where they are contiguous. Even though only a minority of such points of contiguity are welded, the substrate becomes adequately resistant to axial displacing forces generated by exhaust gases passing through the substrate. The substrate may be washcoated prior to making the weld runs.