It seems like "opencell neoprene" is a mainly South African misnomer for "unlined" neoprene, with all neoprene being closed cell. If you can't breath through it--it is closed cell. If you can't literally pour a cup of water through it--it is closed cell.
That's just the way that neoprene is foamed and formed into wetsuit materials. Unlined, which sometimes is called "sharkskin" because it is textured on the outside, is the stretchiest, but a lycra lining on a nitrogen-foamed neoprene is still pretty stretchy.
I was taught to dive in an old conservative program by a former WW2 frogman. And we were taught that if you need a wetsuit, of any kind, you're doing cold water diving, to use the cold water tables not the regular USN dive tables. Except, no one I met had ever heard of that. Until I asked a USN diving medical
officer about it one day, and he said "Absolutely correct." Apparently all or nearly all of the NE US sport diving industry had been diving with the wrong tables for decades, and no one wanted to comment on the emperors fine new wardrobe.
Now of course everyone says "The computer will do that....". Ahuh. One more fine piece of electronics
to leak, run out of batteries, or be recalled.
NOAA and the DoD still require the use of J-valves for tanks
. That same sport diving industry has actually banned
them as unsafe, and refuses to sell, maintain, or deal with them as well.
So much for good information from "industries" that also sell wetsuits.