An assembly for thickening hair has a first adhesive tape, apt to be reversibly adhered on hair, having an adhesive face onto which there are arranged connecting elements of hair extensions of a first plurality of the hair extensions at their respective distal end, and a second adhesive tape, apt to be reversibly adhered on hair, having an adhesive face onto which there are arranged connecting elements of hair extensions of a second plurality of the hair extensions at their respective distal end, the tapes having positioning elements such that the connecting elements of the extensions of said first and second plurality of the hair extensions overlap when the positioning elements are in turn overlapped.