Fiber-reinforced composite springs having a unidirectional fiber wind. The present invention is a cylindrical torsion bar, or a helical tension or compression spring having a core that is either unreinforced, axial-fiber reinforced, or twisted fiber-reinforced, and a continuous-fiber-reinforced composite cladding having most or all of its fibers helically arrayed around the core. The core may be solid or hollow. The sense of the helical winding is that which places the fibers in tension when the spring is used as intended. A cladding fiber winding helix angle of approximately 55.degree. is used with a weak and unreinforced core, while larger or smaller helix angles are used only with a cores having sufficient stiffness to resist axial-normal stress. By carefully selecting the materials for the core and cladding, as well as utilizing a core twist and a fiber winding helix angle appropriate to the application, significant advantages over prior art springs are realized in energy per-unit-volume, energy per-unit-weight, and spring velocity.