  We explore a new action formulation of hyperfluids, fluids with intrinsic
hypermomentum. Brown's Lagrangian for a relativistic perfect fluid is
generalised by incorporating the degrees of freedom encoded in the
hypermomentum tensor, namely by including connection-matter couplings. Quite
interestingly, generic hyperfluids are imperfect, since hypermomentum induces
such effects as bulk and shear viscosities as well as heat fluxes. The various
coefficients that appear in the first order expansion of hydrodynamics can now
be deduced from a Lagrangian formulation, given a geometrical interpretation
and a suggested microscopic description in terms of hypermomentum. This
connection between hypermomentum and dissipative fluids could shed new light on
the physics of relativistic hydrodynamics. The applicability of the new
formalism is demonstrated by exact cosmological solutions.
