sentences:  However, the composite structure can also possibly limit the stability and consequently the range of applications.The most common effect related to ferroelectrets is the direct and inverse piezoelectricity, but in these materials, the effect occurs in a way different from the respective effect in ferroelectric polymers.In ferroelectric polymers, a stress in the 3-direction mainly decreases the distance between the molecular chains, due to the relatively weak van der Waals and electrostatic interactions between chains in comparison to the strong covalent bonds within the chain.