  In the EXOSAT and ROSAT eras a significant number of polars were found to
show a soft/hard X-ray ratio much greater than that expected from the standard
accretion shock model. This was known as the `soft X-ray excess'. We have made
an snapshot survey of polars using XMM-Newton and determined their soft/hard
ratios. We find that less than one in five of systems show a significant soft
X-ray excess, while the rest show ratios consistent with that predicted by the
standard model. We have investigated the discrepancy between this and the
previous investigations by re-examining all the available ROSAT PSPC pointed
observations of polars using more recent calibrations than in the original
studies. We find that these data show an energy balance ratio which is broadly
consistent with that of our XMM-Newton results. We conclude that the previous
studies were affected by the data being less well calibrated. We discuss which
physical mechanisms might give rise to a high soft X-ray excess and whether
systems with high ratios show more variation in soft X-rays. Surprisingly, we
find that 6 out of 21 systems found in a high accretion state did not show a
distinct soft X-ray component. Two systems showed one pole with such a
component and one which did not. Based on the ratio of the observed soft X-ray
to UV flux measurements (which were obtained simultaneously using the Optical
Monitor) we suggest that this is because the reprocessed component in these
systems is cool enough to have moved out of the soft X-ray band and into the
EUV or UV band.
