  {Parker Solar Probe's first solar encounter has revealed the presence of
sudden magnetic field deflections that are called switchbacks and are
associated with proton velocity enhancements in the slow alfv\'{e}nic solar
wind.} {We study their statistical properties with a special focus on their
boundaries.} {Using data from SWEAP and FIELDS we investigate particle and
wavefield properties. The magnetic boundaries are analyzed with the minimum
variance technique.} {Switchbacks are found to be alfv\'{e}nic in 73\% of the
cases and compressible in 27\%. The correlations between magnetic field
magnitude and density fluctuations reveal the existence of both positive and
negative correlations, and the absence of perturbations of the magnetic field
magnitude. Switchbacks do not lead to a magnetic shear in the ambient field.
Their boundaries can be interpreted in terms of rotational or tangential
discontinuities. The former are more frequent.} {Our findings provide
constraints on the possible generation mechanisms of switchbacks, which has to
be able to account also for structures that are not purely alfv\'{e}nic. One of
the possible candidates, among others, manifesting the described
characteristics is the firehose instability.}
