I will present a recent application of the SN 1987A cooling bound to set a constraint on dark flavoured sectors. This is possible thanks to the fact that proto-neutron stars are hot and dense environments where hyperons can be efficiently produced. Therefore a decay of the form Λ→n X_0, where X_0 is a new bosonic dark particle, will be severely constrained. I will explain the ingredients required and the application to flavoured (massless) dark photons, axions and ALPs.