How to distinguish open-pored polymer foam and foam with closed pores?

I was looking at two foam materials, where I had expected one to have closed pores. 


Unfourtunately, the microscope was showing the upper layer of cut cells the same in both cases with no indication of differences in lower levels of the material.


By now, I suspect both are open-pored;


Is the difference clearly defined? 


* If a block of soft material can sustand high pressure based on inner air pressure in cells, the cells are clearly closed.
* If a visual inspection shows mostly incomplete cells, such that parts of cells behind them are visible, it's clearly open pored.
* what about holding gas only at low outer forces?
* Which is similar to the common kitchen sponge, keeping fluid with low pressure, releasing it at high pressure. But here, I expect the pores to be open, and capularry forces to get the water inside.


So, I'd like to know how to tell them appart based on actual mechanical features, and to understand the difference in case they are not trivial.


