The motorised trimmer has a rotary axis (27) for trimming cords (30,32) which are dispensed from a reel (28). The cutting cords extend from a carrying cord (31) to define recesses and projections (35) from its surface (311). The projections and recesses can be mounted as a layer on the support cord. The support cord can be hollow with an elastic and hygroscopic filling. The projections and recesses can be defined in a spiral form.