  Supergiant X-ray binaries usually comprise a neutron star accreting from the
wind of a OB supergiant companion. They are classified as classical systems and
the supergiant fast X-ray transients (SFXTs). The different behavior of these
sub-classes of sources in X-rays, with SFXTs displaying much more pronounced
variability, is usually (at least) partly ascribed to different physical
properties of the massive star clumpy stellar wind. In case of SFXTs, a
systematic investigation of the effects of clumps on flares/outbursts of these
sources has been reported by Bozzo et al. (2017) exploiting the capabilities of
the instruments on-board XMM-Newton to perform a hardness-resolved spectral
analysis on timescales as short as a few hundreds of seconds. In this paper, we
use six XMM-Newton observations of IGR J18027-2016 to extend the above study to
a classical supergiant X-ray binary and compare the findings with those derived
in the case of SFXTs. As these observations of IGR J18027-2016 span different
orbital phases, we also study its X-ray spectral variability on longer
timescales and compare our results with previous publications. Although
obtaining measurements of the clump physical properties from X-ray observations
of accreting supergiant X-ray binaries was already proven to be challenging,
our study shows that similar imprints of clumps are found in the X-ray
observations of the supergiant fast X-ray transients and at least one classical
system, i.e. IGR J18027-2016. This provides interesting perspectives to further
extend this study to many XMM-Newton observations already performed in the
direction of other classical supergiant X-ray binaries.
