This application relates to methods and apparatus for reinforcing fragile portions of a device case. In some embodiments, the device case can be reinforced by a reinforcing member made up of composite extrusions that are embedded within a top edge portion of the stiffening shell. The device shell can be utilized to define and maintain an overall shape of the device case. Composite fibers suitable for use in these embodiments can have high tensile strength and high tensile modulus. The device case can include a single length of embedded twisted composite fibers that extend continuously around the top edge or alternatively can include a number of discrete segments that reinforce particularly fragile portion of the top edge.