Method for manufacturing a balance-spring intended to equip a balance of an horological movement, comprising: a) a step of making available a blank with a core made of Nb-Ti made from an alloy consisting of: - niobium: balance to 100% by weight, - titanium: between 5% and 95% by weight, - traces of one or more elements chosen from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu and Al, each of said elements being present in a quantity between 0 ppm and 1600 ppm by weight, the total quantity formed by all of said elements being between 0% and 0.3% by weight, b) a step of forming a layer of a first material having a first thickness around the blank with the core made of Nb-Ti, c) a step of forming a layer of a second material, said method being characterised in that the layer of the second material has a second thickness greater than the thickness of the layer of the first material around the blank obtained from step b), the first and second materials being chosen so that the second material is able to be selectively eliminated physically or chemically without substantially attacking the first material, d) a step of forming the blank in several sequences comprising: d1) a succession of forming-stage steps for bringing the blank obtained in step c) to a determined diameter called calibration diameter and d2) a succession of steps of flat rolling the round blank obtained in step d1), e) a step of cutting the rolled wire into blades having a determined length, f) a step of winding to form the balance-spring, g) a step of final heat treatment of the balance-spring, and wherein said method further comprises a step h) of removing said layer of the second material formed in step c), when the blank has reached a diameter such that it is still possible to pass said blank at least through one draw-plate with a degree of elongation of the blank of approximately 10% before the first rolling step d2) or at the latest before the last stage of step d2). a) a step of making available a blank with a core made of Nb-Ti made from an alloy consisting of: - niobium: balance to 100% by weight, - titanium: between 5% and 95% by weight, - traces of one or more elements chosen from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu and Al, each of said elements being present in a quantity between 0 ppm and 1600 ppm by weight, the total quantity formed by all of said elements being between 0% and 0.3% by weight, - niobium: balance to 100% by weight, - titanium: between 5% and 95% by weight, - traces of one or more elements chosen from the group consisting of O, H, C, Fe, Ta, N, Ni, Si, Cu and Al, each of said elements being present in a quantity between 0 ppm and 1600 ppm by weight, the total quantity formed by all of said elements being between 0% and 0.3% by weight, b) a step of forming a layer of a first material having a first thickness around the blank with the core made of Nb-Ti, c) a step of forming a layer of a second material, said method being characterised in that the layer of the second material has a second thickness greater than the thickness of the layer of the first material around the blank obtained from step b), the first and second materials being chosen so that the second material is able to be selectively eliminated physically or chemically without substantially attacking the first material, d) a step of forming the blank in several sequences comprising: d1) a succession of forming-stage steps for bringing the blank obtained in step c) to a determined diameter called calibration diameter and d2) a succession of steps of flat rolling the round blank obtained in step d1), d1) a succession of forming-stage steps for bringing the blank obtained in step c) to a determined diameter called calibration diameter and d2) a succession of steps of flat rolling the round blank obtained in step d1), e) a step of cutting the rolled wire into blades having a determined length, f) a step of winding to form the balance-spring, g) a step of final heat treatment of the balance-spring,