  We show that simple thermodynamic conditions determine, to a great extent,
the equation of state and dynamics of cosmic defects of arbitrary
dimensionality. We use these conditions to provide a more direct derivation of
the Velocity-dependent One-Scale (VOS) model for the macroscopic dynamics of
topological defects of arbitrary dimensionality in a $N+1$-dimensional
homogeneous and isotropic universe. We parameterize the modifications to the
VOS model associated to the interaction of the topological defects with other
fields, including, in particular, a new dynamical degree of freedom associated
to the variation of the mass per unit $p$-area of the defects, and compute the
corresponding scaling solutions. The observational impact of this new dynamical
degree of freedom is also briefly discussed.
