The invention relates to an apparatus (10) for crimping a sheet (40) of material, the apparatus comprising a first and second facing crimping roller (11, 21) defining a first and second rotation axis, respectively, the first roller including: •a first plurality of circumferential ridges (16), each ridge defining a ridge amplitude; •wherein each of said first plurality of ridges is interrupted along its circumferential extension forming an interruption gap where for a given interruption angle an amplitude of the ridge differs from the ridge amplitude in the remaining circumferential extension of the ridge; •wherein said plurality of interruption gaps forms an interruption band defining a direction of extension, said direction of extension being angled with respect to a direction defined by the first rotation axis of an angle comprised between about 2° to about 25°. The invention also relates to a method for crimping a sheet of material as well as a crimped sheet of material and a rod made of a crimped sheet.