Layer composites containing adaptive polydomain components are considered. Polydomain structures can be result of constrained phase transformation. Polydomain structures consist of periodically alternating layers of different phases or differently oriented domains of product phase. The domain interface movement enables an additional mode of deformation. The theory predicts unusual physic and mechanical properties of composites, particularly, considerable decrease of the effective elastic moduli of composites, nonlinear stress-strain relations, critical behavior at decreasing thickness of an active layer. For ferroelectric or ferromagnetic polydomain components superelasticity can be governed and stiffed by the bias electric or magnetic field.