Despite the observed increases in the HFR, the thickness of both membranes (Figure ) was found to decrease during the stability test, just as was found with the lab-based study (Section 2.3). However, the short scan times of the operando μ-CT increased the temporal resolution of the tmemb measurements. For the Fumasep® equipped cell, the rate of membrane thinning was non-linear: tmemb decreased quickly at first with the rate of thinning slowing towards the end of the 20 h test where the membrane had lost 58 ± 6% of the original thickness, close to the 53 ± 3% measured in the lab-based μ-CT study. A similar trend was observed for the calculated σmemb shown in Figure .