The expression for the modulus of elasticity of a flat, multicomponent, partially open, nonsymmetric thick film was derived. It was shown that the Gibbs elasticity of a thick film exists outside of the dependence on its thickness and is guaranteed by the thermodynamic stability of the bulk phase and the surface layers of the film. It was established that under isothermal and isobaric conditions any thick film with no less than two immobile components exhibits Gibbs elasticity.