Our previous work measured H2O diffusion on CALF-20 using only He as a carrier gas. In Figure , the impact of N2 on H2O diffusion was examined. This experiment was conducted at 5% RH using a carrier gas, which was 17% He and 83% N2. The presence of N2 appears to have caused a mixed-gas behavior where data points in the high-frequency range occur beyond the control response (circled in Figure ). CSFR measurements were conducted with sinusoidal perturbations at the mid to high-frequency range to investigate the behavior in more detail. These measurements also observed this effect; therefore, it was concluded that this behavior is not an artifact of the FT-CSFR method but rather likely a mixed-gas behavior. Because singlecomponent models cannot capture this behavior, no rates are reported for these experiments. More complex mixed-gas FR models have been reported and subsequent works may help deconvolute this data. Even in the case of carbon materials known to adsorb N2 at ambient conditions, the impact of N2 on the diffusion of other species has not been studied extensively. For example, in some cases, it has been found that either diffusion cross terms are negligible or that the impact of N2 on the diffusion of the other components can be neglected. Very few examples have been found where cross terms are significant, such as the diffusion of mixtures of O2 and N2 in carbon molecular sieves. The data collected in the current work indicate that cross-term diffusion coefficients in CALF-20 for the gas systems examined may be important.