The transition from PFAS-based aqueous film-forming foams (AFFF) to fluorine-free firefighting foams (F3) creates a need for formulations that provide effective fire suppression, fuel resistance, and burnback protection without fluorinated surfactants. These projects investigate the interfacial and chemical mechanisms that control F3 performance and identify strategies to improve foam stability and fire suppression. Research combines fire testing, interfacial characterization, rheology, molecular dynamics simulations, and analytical chemistry to evaluate how surfactant composition and fuel-foam interactions affect foam formation, stability, fuel pick-up, emulsification, and vapor transport. Catanionic mixtures of anionic and cationic surfactants are being evaluated for their ability to form interfacial assemblies and bilayer vesicles that reduce surface tension and potentially slow foam coarsening and coalescence. Complementary studies examine fuel pick-up and three-phase foam flammability as factors that can limit F3 effectiveness, particularly for gasoline fires and under demanding environmental conditions. Results are being used to develop interfacial engineering and emulsification strategies to increase fuel tolerance, improve burnback resistance, and narrow the performance gap between F3 and conventional AFFF for DoW fire suppression applications.