Earlier research with phosphorus-based molecular fortifiers showed a range of improvements in physical, thermal, and mechanical properties. This contribution introduces sulfur- and carbon-based molecules into a model epoxy network for comparison. Similar improvements in rheological, physical, and select mechanical properties are found between the phosphorus and sulfur- and carbon-based fortifiers. Thermal properties are not enhanced with the sulfur and carbon fortifiers. Two of the sulfur compounds phase separate upon cure of the epoxy network and show unique behavior. In addition, infrared spectroscopy is performed to identify possible mechanisms of reinforcement.