This paper starts from a toy model for inflation in a class of modified theories of gravity in the metric formalism. Instead of the standard procedure—assuming a non-linear Lagrangian f(R) in the Jordan frame—we start from a simple ϕ2 potential in the Einstein frame and investigate the corresponding f(R) in the former picture. The addition of an ad-hoc Cosmological Constant in the Einstein frame leads to a Thermodynamical interpretation of this physical system, which allows further insight on its (meta)stability and evolution.