  The partition function of two-dimensional solitons in a heat bath of mesons
is worked out to one-loop. For temperatures large compared to the meson mass,
the free energy is dominated by the meson-soliton bound states and the zero
modes, a consequence of Levinson's theorem. Using the Bethe-Uhlenbeck formula
we compare the soliton energy-shift to the shift expected in the pole mass
using a virial expansion. We construct the partition function associated to a
fast moving soliton at finite temperature, and found that the soliton thermal
inertial mass is no longer constrained by Poincare's symmetry. At finite
temperature, the concept of quasiparticles is process dependent.
