  We perform a model independent study of the neutrino momentum distribution at
freeze-out, treating the freeze-out temperature as a free parameter. Our
results imply that measurement of neutrino reheating, as characterized by the
measurement of the effective number of neutrinos $N_\nu$, amounts to the
determination of the neutrino kinetic freeze-out temperature within the context
of the standard model of particle physics where the number of neutrino flavors
is fixed and no other massless (fractional) particles arise. At temperatures on
the order of the neutrino mass, we show how cosmic background neutrino
properties i.e. energy density, pressure, particle density, are modified in a
physically consistent way as a function of neutrino mass and $N_\nu$.
