In this case, the rate in He is 5.7x faster than with N2 present. When comparing LDF rates to micropore diffusion rates, the comparison is less straightforward. A common approximation for LDF coefficients from micropore diffusion rates is to assume 15 times the micropore diffusion rate constant as the LDF rate, as given by where 𝐷 is the diffusivity, 𝑟 is the characteristic length, 𝐷 𝑟 2 is the micropore diffusion rate constant from CSFR, and 𝑘 is the LDF coefficient. When this approximation is made, and the rates are compared for 2% and 4% CO2, the rates in He are 4.8 and 8.7x faster than with N2, respectively. Therefore, it appears that N2 slows the diffusion of CO2 in CALF-20, though more work is needed to understand the complete mixed-gas diffusion behavior. Specifically, although CSFR has the capability to quantify mixed-gas diffusion along with the diffusion cross terms, mixed-gas isotherms at various concentrations would be necessary to correctly capture the data, and the measurement of these isotherms is beyond the scope of the current work.