We consider the impact of the mechanical behaviour of polymeric coatings on glass strengthening. We have performed rupture stress measurements and compared the strengthening measured in the rubbery state and the glassy state. We evidence a moderate decrease of the strengthening when the temperature exceeds the glass transition temperature of the coating. Based on the predictions of crack bridging models, we show that the limited difference of strengthening between glassy and rubbery states can be understood if confinement of the polymer inside the crack is taken into account. Similarly, our results suggest that confinement severely limits the shear deformation of polymeric coatings and suppresses viscoelastic dissipation.