While it is often assumed that liquid-vapor interfaces in nonequilibrium processes are in states of local thermodynamic equilibrium, this might not be the case for strong deviations from equilibrium. Clausius-Clapeyron equations for bulk properties yield a consistently defined temperature of the interface that is close to the liquid bulk temperature. The alternative interface temperature defined through the surface tension will be different for stronger nonequilibrium processes. Structural variables are introduced to extend the thermodynamic description of interfaces to a wider range of processes. Interfacial resistivities will depend on interface temperature as well as mass and heat flux through the interface.