  We investigated helium-mediated translational and rotational thermalization
of the aluminum monofluoride (AlF) molecule at cryogenic temperatures via a new
$ab \ initio$ potential energy surface (PES) and quantum multichannel
scattering theory. Our examination of the elastic and rotationally inelastic
channels revealed that helium is an efficient quencher of AlF at temperatures
relevant to buffer gas cooling experiments ($\sim1$ mK to $10$ K). We also
showed that this conclusion is robust against possible inaccuracies of the PES.
