The microscopic effect of capillary causes fluid exchange between closed pores and fluid exchange between fine network channels and thick network channels.

There are evenly distributed open pores and closed pores Inside sample, evenly distributed closed pores not only reduce the Wa, but also increase the resistance to freezing and thawing.

It is found that the transition layer composed of closed-cell with tight and smaller pore-size pores makes the asymmetriC membrane benefit of gas separation.