The present invention relates to fiber glass strands, yarns, fabrics, composites, prepregs, laminates, fiber-metal laminates, and other products incorporating glass fibers formed from glass compositions. The glass fibers, in some embodiments, are incorporated into composites that can be used in reinforcement applications. Glass fibers formed from some embodiments of the glass compositions can have certain desirable properties that can include, for example, desirable electrical properties (e.g. low Dk) or desirable mechanical properties (e.g., specific strength).