The radius of curvature that an optical Fiber can bend without sustaining damage.

Bend radius, which is measured to the inside curvature, is the minimum radius one can bend a fiber optic Cable without kinking it, damaging it, or shortening its life. The smaller the bend radius, the greater the material flexibility (as the radius of curvature decreases, the curvature increases). A Minimum Bend Radius is the radius below which an Optical Fiber or fiber-optic cable should not be bent. Larger radii bends are easier to pull, and put less Strain on the cable being pulled.

The minimum bend radius is of particular importance in the handling of fiber-optic Cables and varies with different cable designs. The manufacturer should specify the minimum radius to which the cable may safely be bent during installation, and for the long term. The former is somewhat shorter than the latter. The minimum bend radius is in general also a function of tensile stresses during installation, while being bent around a sheave while the fiber or cable is under tension. If no minimum bend radius is specified, one is usually safe in assuming a minimum long-term low-stress radius not less than 15 times the cable diameter.