where \(h\) is the actuator height at rest,\(l_{e}\left(\alpha\right)\) and \(l_{p}\left(\alpha\right)\) are the length of the zipped and unzipped portions of the pouch, respectively. Since the liquid volume is constant during deformation, so is the area\(A\) in each 2D cross section. \(l_{e}\left(\alpha\right)\) and\(l_{p}\left(\alpha\right)\) are a function of the area \(A\) and of the angle \(\alpha\)