The hysteresis between the adsorption isotherm and desorption isotherm is thouAdditionally, there is a phenomenon that the desorption isotherm is closed to the adsorption isotherm side at the same equilibrium pressure even if the pore size is changed (without the special case of low pressure hysteresis). This phenomenon shows that the reason of desorption isotherm to be closed is not related to the pore size and is due to the adsorptive physical property at the adsorption temperature. This behavior is caused by the cavitations of adsorption phase in the pores. The pore size distribution analysis obtained from the desorption isotherm always has the peak of 3.4nm pore due to the pressure of cavitations. This pore needs to be ignored when using the desorption of N2 isotherm at 77K because this is not related to the pore condensation on the materialht to be caused by the gradual desorption mechanism (percolation theory) due to the different size pores being combined. This percolation theory suggests that the pore size distribution obtained from the desorption isotherm is problematic to be used. It is commonly said that the pore size distribution obtained from the adsorption isotherm has less problems and is closer to the true value.