Bound fraction as a function of gas removal velocity for different ε_SFE, here for clusters with an initial stellar mass of 10⁴M_⊙ and a HMR of 0.3 pc. Approximating the gas removal to be instantaneous might make the assumption of an unusually high ε_SFE necessary, as otherwise simulations might not have any surviving cluster after gas expulsion. Every data point corresponds to a single simulation.