  We study a nonlinear generalization of a free boundary problem that arises in
the context of thermal insulation. We consider two open sets $\Omega\subseteq
A$, and we search for an optimal $A$ in order to minimize a non-linear energy
functional, whose minimizers $u$ satisfy the following conditions: $\Delta_p
u=0$ inside $A\setminus\Omega$, $u=1$ in $\Omega$, and a nonlinear Robin-like
boundary $(p,q)$-condition on the free boundary $\partial A$. We study the
variational formulation of the problem in SBV, and we prove that, under
suitable conditions on the exponents $p$ and $q$, a minimizer exists and its
jump set satisfies uniform density estimates.
