  We present a novel baryogenesis mechanism in which the asymmetry is sourced
from heavy particles which either gain their mass or are created during bubble
expansion in a strong first order phase transition. These particles then decay
in a CP and baryon number violating way inside the bubble. The particles are
inherently out-of-equilibrium and sufficiently dilute after wall crossing so
the third Sakharov condition is easily met. Washout is avoided provided the
reheat temperature is sufficiently below the scale of the heavy particles. The
mechanism relies on moderate supercooling and relativistic walls which -- in
contrast to electroweak baryogenesis -- generically leads to a sizable
gravitational wave signal, although in the simplest realisations at frequencies
beyond upcoming detectors. We present a simple example model and discuss the
restrictions on the parameter space for the mechanism to be successful. We find
that high reheat temperatures $T_{\rm RH} \gtrsim 10^{10}$ GeV are generally
preferred, whereas stronger supercooling allows for temperatures as low as
$T_{\rm RH} \sim 10^{6}$ GeV, provided the vacuum energy density is
sufficiently suppressed. We briefly comment on using resonantly enhanced CP
violation to achieve even lower scales.
