  We show that interactions between axion-like particles (ALPs) and
co-dimension one defects, such as phase-transition bubble walls and solitonic
domain walls, can lead to important changes in the evolution of both walls and
ALPs. The leading effect arises from the change in the ALP decay constant
across the interface, which naturally follows from shift-symmetric interactions
with the corresponding order parameter. Specifically, we show that for thin
walls moving relativistically, an ALP background -- such as e.g. axion dark
matter -- gives rise to a frictional force on the interface that is
proportional to $\gamma^2$, with $\gamma$ the Lorentz factor of the wall, and
that this effect is present in both the oscillating and frozen axion regimes.
We explore the broader consequences of this effect for bubble and domain walls
in the early universe, and show that this source of friction can be present
even in the absent of a conventional medium such as radiation or matter.
Possible implications include modifications to the dynamics of bubble and
domain walls and their corresponding gravitational wave signatures, as well as
the generation of a dark radiation component of ALPs in the form of
ultra-relativistic `axion shells' with Lorentz factor $\gamma_\text{shell}
\simeq 2\gamma^2 \gg 1$ that may remain relativistic until the present day.
