The values of tmemb and σmemb for Fumasep® FAA-3 from the lab, operando and reference tests are summarised in Table . For the Fumasep® membrane, σmemb decreased by 97.5 ± 0.3% by the end of the stability test, significantly more degraded than the 62 ± 3% reduction in σmemb measured in the lab-based study. The extra loss of σmemb was attributed to the damage caused by exposure to synchrotron radiation as shown by the sharp decrease in σmemb during each period of OCP when μ-CT scans were performed (Figure ). It should be noted that in addition to the σmemb, contact resistance also affected the magnitude of the HFR. Because the ME-cell design is such that compression is fixed when the cell is first assembled, the contact resistance likely increased as the membrane thinned, as was observed with the HFR in the lab-based study shown in Figure .