The energy leaking through a slot in the hohlraum filled with low-<i>Z</i> foams is a typical dynamic problem of the ablated high-<i>Z</i> plasmas. In this paper, we develop a simplified one-dimensional model to study the expansion-reverse process of the ablated Au plasmas, which corresponds to the closing-reopening process of a slot. Our work shows that its physical mechanism is the ablation pressure competing with radiation pressure difference and the material pressure of low-<i>Z</i> foams. The analytical formulas for the reverse time and reverse distance of the Au plasma are deduced, respectively, indicating that the cubic value for each of both peak temperatures is proportional to the density of the low-<i>Z</i> foams. The main conclusions of analytic theory are verified by numerical simulation through using the modified radiation-hydrodynamic program MULTI. It is shown that the power exponents of scaling law in high-<i>Z</i> plasma ablation keep unchanged in a wide range of density of low-<i>Z</i> foams. The range of validity of the model is discussed.