  The large temperature difference between cold gas clouds around galaxies and
the hot halos that they are moving through suggests that thermal conduction
could play an important role in the circumgalactic medium. However, thermal
conduction in the presence of a magnetic field is highly anisotropic, being
strongly suppressed in the direction perpendicular to the magnetic field lines.
This is commonly modelled by using a simple prescription that assumes that
thermal conduction is isotropic at a certain efficiency $f<1$, but its precise
value is largely unconstrained. We investigate the efficiency of thermal
conduction by comparing the evolution of 3D hydrodynamical (HD) simulations of
cold clouds moving through a hot medium, using artificially suppressed
isotropic thermal conduction (with $f$), against 3D magnetohydrodynamical (MHD)
simulations with (true) anisotropic thermal conduction. Our main diagnostic is
the time evolution of the amount of cold gas in conditions representative of
the lower (close to the disc) circumgalactic medium of a Milky Way-like galaxy.
We find that in almost every HD and MHD run, the amount of cold gas increases
with time, indicating that hot gas condensation is an important phenomenon that
can contribute to gas accretion onto galaxies. For the most realistic
orientations of the magnetic field with respect to the cloud motion we find
that $f$ is in the range 0.03 -- 0.15. Thermal conduction is thus always highly
suppressed, but its effect on the cloud evolution is generally not negligible.
