  Viscous flow of interacting electrons in two dimensional materials features a
bunch of exotic effects. A model resembling the Navier-Stokes equation for
classical fluids accounts for them in the so called hydrodynamic regime. We
performed a detailed analysis of the physical conditions to achieve electron
hydrodynamic transport and found three new alternative routes: favouring
frequent inelastic collisions, the application of a magnetic field or a
high-frequency electric field. As a mayor conclusion, we show that the
conventional requirement of frequent electron-electron collisions is too
restrictive and, as a consequence, materials and phenomena to be described
using hydrodynamics are widened. In view of our results, we discuss recent
experimental evidence on viscous flow and point out alternative avenues to
reduce electric dissipation in optimized devices.
