Experimental APL measurements show a decrease of ~14 Å 2 for SOPC (which given the nature of the 4-to-1 mapping of the Martini acyl chain beads makes it comparable to POPC) upon the addition of 28 % cholesterol at 310 K 111 . This is in line with both Martini and AA models tested here, given the known difficulties in determining APL measurements experimentally 112 . As expected from experimental results 1 , cholesterol also had a very strong ordering effect in both PC bilayers (Figure ). This ordering effect was stronger in saturated DPPC bilayers than in POPC bilayers, which required higher cholesterol concentrations to achieve substantial increases in acyl chain order. Both Martini 2 and 3 models showed identical responses in acyl chain order. Overall, these results point out that our cholesterol model is impacting simple PC bilayers well in agreement with the existing experimental and AA MD results. This test set was also run with the OpenMM implementation of the new Martini 3 cholesterol model (Supplementary Figure ), replicating the conditions of the same simulations run in GROMACS. Our results show a dependence of membrane thickness, APL, and acyl chain order with increasing cholesterol concentration, in a manner that is consistent with results obtained in GROMACS simulations, further validating the OpenMM implementation.