A vaso-occlusive device is formed from an elongate strand of material wound by a winding process into a helical coil having a length, wherein one or more discrete sections of the coil along its length were subjected to less mechanical stress or strain than a remainder of the coil during the winding process, such that each of the one or more discrete sections has a lower stiffness and greater flexibility than a respective stiffness and flexibility of the remainder of the coil, and such that each of the discrete one or more sections acts as a bending location along the length of the coil when the coil is delivered into an aneurysm.
