Polydomain materials with periodic (modulated) domain structures are of potential practical importance since they can possess unique and desirable mechanical and physical properties. A twin related domain formation can be a result of constrained structural, ferroelectric or ferromagnetic transformations. The thermodynamic theory on the deformation of layer composites containing a polydomain (polytwin) ferroelectric component is analyzed. The deformation of the layer composite under different directional electric fields and constraints is calculated.