  We consider the effect of relativistic boosts on single particle Gaussian
wave packets. The coherence of the wave function as measured by the boosted
observer is studied as a function of the momentum and the boost parameter.
Using various formulations of coherence it is shown that in general the
coherence decays with the increase of the momentum of the state, as well as the
boost applied to it. Employing a basis-independent formulation, we show
however, that coherence may be preserved even for large boosts applied on
narrow uncertainty wave packets. Our result is exemplified quantitatively for
practically realizable neutron wave functions.
