it is a very thin layer of Poron attached to the neoprene. Also to consider is there are different thicknesses of the neoprene. Could make difference to concussions.
Used mostly CCM for the past 10 years, closer is always a bit of a problem.
Best from the past was TPS by Wilcox. now working with Kenesky.
Currently Ultrasonic. Very comfortable, easy closer, deep pocket.