  The growing sample of LIGO--Virgo black holes (BHs) opens new perspectives
for the study of massive binary evolution. Here, we study the impact of mass
accretion efficiency and common envelope on the properties of binary BH (BBH)
mergers, by means of population synthesis simulations. We model mass accretion
efficiency with the parameter $f_{\rm MT}\in[0.05,1]$, which represents the
fraction of mass lost from the donor which is effectively accreted by the
companion. Lower values of $f_{\rm MT}$ result in lower BBH merger rate
densities and produce mass spectra skewed towards lower BH masses. Our
hierarchical Bayesian analysis, applied to BBH mergers in the first and second
gravitational wave transient catalogue, yields zero support for values of
$f_{\rm MT}\lesssim{}0.6$, with a lower boundary of the 99\% credible intervals
equal to $f_{\rm MT}= 0.59$. This result holds for all the values of the
common-envelope efficiency parameter we considered in this study $\alpha_{\rm
CE} \in [1,10]$. This confirms that gravitational-wave data can be used to put
constraints on several uncertain binary evolution processes.
