Abstract: A method for providing a fibre with an additional length in secondary mantling of an optical fibre, according to which an optical fibre is coated by means of extrusion (3) with a secondary mantle allowing an axial movement between the fibre and the mantle, the mantled fibre (6) is drawn (10) axially forwards after the coating, the mantle is stretched (11) axially with respect to the fibre, and the elongation of the mantle is allowed to relax (12) together with the fibre so that the fibre is longer than the mantle in the relaxed mantled fibre, after which the relaxed mantled fibre is winded on a coil (13). The fibre and mantle are locked (11) axially stationary to each other during the advancing of the mantled fibre (6) before the relaxation of the elongation of the mantle, and the mantle is subjected to a retardation (10) during the advancing of the mantled fibre for stretching the mantle with respect to the fibre before locking of the fibre and mantle.