A filament or fibre (10), comprising an elongate core (11) having a core axis, and a substance (13) having at least one electrically modulatable optical characteristic, covering at least a portion of the core. The filament or fibre further comprising an electrical stimulation means (12) adapted to produce an electric field extending in a direction substantially parallel to the core axis or in a direction extending substantially circumferentially about the core axis, wherein the electric field electrically induces a change in the optical characteristic of the substance, thereby changing the visual appearance of the filament or fibre. |