  We study anisotropic fluid dynamics derived from the Boltzmann equation based
on a particular choice for the anisotropic distribution function within a
boost-invariant expansion of the fluid in one spatial dimension. In order to
close the conservation equations we need to choose an additional moment of the
Boltzmann equation. We discuss the influence of this choice of closure on the
time evolution of fluid-dynamical variables and search for the best agreement
to the solution of the Boltzmann equation in the relaxation-time approximation.
